Roy's plainly visible at least. As is everyone else we see. But no bodily worries, not even those outsiders have to contend with, seem to be a thing for him:
http://www.giantitp.com/comics/oots0499.html
I would suggest that souls, unlike lantern archons, can't actually be harmed normally - they're not "creatures" by D&D standards, and don't actually have stats.
EDIT: Apparently, The Giant has said souls in the afterlife are interactable with, by adventurers:
http://www.giantitp.com/forums/showt...-After-vs-Life
you will never improve at any skill you know, never have a say in what happens in the world, never have children if you haven't already, never talk to anyone with a different point of view, never experience any real risk, never visit anywhere else, and never see any friends or family members who did not share the exact same shade of alignment as you. Oh, and you can still be destroyed by evil adventurers, but you never get any better at defending yourself.
And that's the Lawful Good afterlife.so Roy's question "can I be killed in this form" has an answer - Yes:Dead souls cannot earn XP, gain levels, learn feats, or increase skills.
http://www.giantitp.com/comics/oots0497.html
So by implication, prior to becoming an Outsider and a petitioner, you weren't one before.
Other features of a Dead Soul as opposed to a petitioner, I would suggest - not having a heartbeat, not having to breathe, and not having to move their legs to get around:
http://www.giantitp.com/comics/oots0665.html
http://www.d20srd.org/srd/typesSubty...m#outsiderType
Outsiders, by contrast, qualify as living creatures - and they do have to breathe.