Yes, if it is an engine update it will break every mod the servers currently run. For popular things this could be fine but some stuff like wcs could be permanently broken. Also much of our custom hacks/scripts may be broken.
Depends on the new engine, and if the mod is still actively maintained. It seems that WCS has a number of coders, but maybe not one central person to organize it all. ZombieMod saw a release last year, and the main developer for it appears to be posting on their foum every once in a while. I'd bank on ZM being updated before WCS, but I'm not intimately familiar with either project.
Manimod is updated for use with TF2, which uses the orange box engine, so it should be easily adaptable to the new CS:S beta.
Kiro : us fireyes got dumb by his girl that y he is suck
Well that'd be the third thing they've fucked up if they do, do it and to one of their most popular games too.
To say the least its a very, VERY BAD IDEA.
However making it a separate game called CS:S 07 wouldn't be.
I'd put my money on it being a behind-the-scenes update and not grapical, which doesn't bother me one little bit.
We can only hope it doesn't break the mods, you'd have A LOT of people raging.
That is, unless they release it as a seperate game.
EDIT: Just noticed there was a video that was posted...
Looks like it's not a cosmetic update, no new graphics, but I really like the idea of achievements finally coming to CSS