They're not daft, they're the things we all think (along with, if my waters break in the supermarket, will I flood the place? And if they go in M&S is it true I get free groceries for a year?!!)
In answer, I would say that it might be difficult to clean it off the couch if there is any blood present, otherwise I would assume a good scrub would make it ok.
Yes you can have a bath if they go... I'm assuming this, cos if you were having a waterbirth it would be ok
And there is a chance you might not know when they go, I didn't even notice them going with dd1 as was in full labour, but withh dd2 they went just as I hit the 'I need to push!' stage. Had been in labour for a while with both, I think it's unusual for them to break without warning. HTH