I actually don't think the live action project will ever happen, or if it does, it'll be a re-imagining some 20 to 30 years down the road with a completely different cast. A lot of it is because most of the cast isn't nearly as interested as fans think they are, if you go by the throw-away comments they've made over the years.

As for the Xander storyline in the comics, I'm not convinced that it's so much an actor being replaced by a paper doll that's at issue as it is the lack of network interference (remember UPN practically ordered Joss to use "Spike" more in Season 7 -- remember the memo that got touted all over hell and creation when it was leaked?) as well as a changed situation opening up possibilities.

*shrug*

It's impossible to speculate since we don't actually know, well, anything. I'd put the re-appearance of anything of a live-action very, very low.