I am planning to put it on the DM's Guild after doing some cleanup :)
I can't say "Castlevania" in the title, and "Demon Castle Dracula" would be both misleading (in English) and too obscure for most people to connect. I'm still trying to figure out a short, punchy name.

After thinking about it overnight, I realized that I should simply point out, at the start of the next session, that they have taken a long rest only about 2 hours ago, which means they do not have the ability to take another one any time soon.
I think that'll get them to think about their resources and realize that "kill it all" is not compatible with "have spell slots and daily resources available to continue." If they do try to hole up and wait for a while, I'll have a skeleton dragon land on that 5' wide bridge to the central keep.

I do have a partial recharge ("you get the effects of a short rest and 1/2 your expended daily resources back") planned for them after Death and before Dracula.