2 players in 4e

[quiet1mi]

what to do what to do... instead of 4 players I only have 2...

do I just continue on and have npc fill the spot?
do I just continue on and cut the xp/cr in half per encounter?
do I just continue on and ignore the glaring problem of half the good guys while hoping for the best?
do I just continue on by giving them more points to make their character with?

[Raewyn]

If they're amenable to the idea, you could let your players each run a 2nd character. It beats having to run two NPCs and the campaign at the same time.

[Jeramiahh]

I'm running a pair of solo games, and, besides giving them twice the starting cash/equipment, they're otherwise core characters. Encounters are noticeably trimmed down; One has faced (and beaten) a pair of level 5 minions and a level 3 Artillery, while the other is currently fighting 4 level 3 minions, one soldier, and one artillery; both are level 6, a warlock/rogue, and a paladin.

So far, so good; the first will likely need to use one or two healing surges to recover to full, and the paladin is yet to be damaged, though we're only a couple rounds in.

[Tengu_temp]

4e seems to be very small group-friendly as long as there's a leader or the characters have healing potions. Just scale down the encouunters to the point where the characters get as much experience as they'd get in a larger group and with a larger enemy force - remember that an average encounter for X characters consists of X ordinary monsters of their level.

[NecroRebel]

Simplest way to do it is probably to have both players make and play 2 characters concurrently, assuming they're up to it.

1/2 cr isn't really what you want. That'll be too low after only a few levels. Probably cr 2 or 3 lower than you would normally want for a full party.

If you do have only 2 characters, you should probably strongly suggest a Leader and a Striker, maybe with multiclassing into Defender and Leader, respectively. They can almost certainly do without a Controller.

In the alternative, you could try converting the 3.5e Gestalt rules. Give them a free multiclass feat at level 1, an extra at-will from their multiclass, and give them the other multiclass feats for free when they become available, except as bonus powers instead of replacing powers. Action economy will still be precious for them, but it'll give more variety and hopefully will allow them to cover weaknesses that they would otherwise have, and would probably let them count as a 3.5 or so-man party.

Or, you yourself as DM could put in a DMPC, ideally of a character type that doesn't really do much; Defender and Leader seem to be the best roles for this IMHO, especially the Defender who largely just stands around looking threatening. A DMPC should never have high knowledge-type skills, so Wizard is a big no-no, and they should never be outdoing the players, so Warlock is probably out too (they tend to be the most damaging, which is the most obvious combat contribution).

[ghost_warlock]

You could consider making a homebrewed version of gestalt. Give them a few more points for their attributes (24-26 or so).

Hit points would be based on whichever class allots the highest. Take the best adjustment for each defense from either class (eg., a fighter//rogue would have +2 Fort, +2 Ref, +0 Will while a cleric//paladin would have +1 Fort, +1 Ref, +2 Will).

Choose powers for each class as normal, thus characters will have more at-will/encounter/dailies than normal but can still only use 1/round (usually).

For skills, pool class skills and let the character select a number of trained skills equal to whichever class provides the most and then let the character have one extra.

Feats as normal.

The characters still follow all rules of their class. So if a character plays a warlock//wizard, only the wizard dailies and utilities go in the spellbook, not the warlock powers. Characters who mark opponents can still only have one opponent marked as usual, even if they take two classes that allow marking (eg., fighter/paladin).

Ideally, the players will choose classes in such a way that they'll retain access to each of the four PC roles.

Keep in mind, also, that the 4e rules assume a 5-character party, so even with this gestalt option, the characters might still might not be able to handle certain monsters/combos. They'll still a two-person party, and are restricted in how much they can accomplish in a single round as such, they're just a bit tougher and versatile individually.

[Viruzzo]

If they're amenable to the idea, you could let your players each run a 2nd character.
I too think that's the best option, obviously it has to fit with your campaign (but you'll manage). It's also a good way to acquire experience with more 4e classes at the same time.

[Covered In Bees]

Have them each run two characters. For bonus points, the characters need to have some kind of close relationship--siblings, husband and wife, mentor and student, etc.

[amanamana]

Don't worry about that! Listen the Tengu (even if the japanese say you shouldn't). If you got 2 pc's, use 2 monsters instead of 4. Use an elite instead of a solo. That way you can stick with the level apropriate.
Just be sure you've got one leader with the group, cause this is serious: they will need it, otherwise you better be throwing buckets of healings potions to them.
I'm DMing one game like this just now. My players wanted to play a ranger and a mage, so a gathered them with a tactical warlord, just to be sure. Didn't want them to HAVE to take a character they didn' wanted to, so the warlord will be there for the healing and moving, cause I didn't want my NPC to have a huge charisma and own the social situations.
best of luck,
amanamana.

[Jarlax]

its true you can indeed run with 2 PCs, combat is always at a 1:1 ratio for regular mobs. in an encounter 1 monster of level X for every PC of level X.

don't use solos and your sitting pretty. you can also derive your encounter XP totals by multiplying the exp reward for a single monster of your players level(page 56, dmg) by 2.

for your players they will need to be careful with their class choices. a warlord fits quite well into the tank/healer role leaving a second player to choose what they like. but any defender+leader combo is fine.

[Hopeless]

what to do what to do... instead of 4 players I only have 2...

do I just continue on and have npc fill the spot?
do I just continue on and cut the xp/cr in half per encounter?
do I just continue on and ignore the glaring problem of half the good guys while hoping for the best?
do I just continue on by giving them more points to make their character with?

It is possible to run a game with just two players I'd recommend having an npc character or two available in case they prefer characters without access to healing or some skills that should be useful.
Maybe even have an ally whose an npc warlord or cleric who they deal with for their missions say like in Eberron where they often have patrons hiring them to investigate rumours and situations and then design the game taking note there is only 2 of them.

What do they want to play by the way?