As you suspect, any play will accelerate wear - it's called attrition in geology; the difference nice constant pressure and being repeatedly hit.....
It could be that permanent damage will occur, though that depends on whether the wear is in the replacement parts (e.g., bushes) or between those parts and the bike. Is there any way you might be able to squeeze some more grease in through the nipple? It might slow the wear up a bit, long enough to get to a better workshop.
Either way, I'm sure any damage will be repairable, but I would get a set sent out and do it yourself; if there is play, the old one won't be too difficult to get out. If you can't do it you might still be able to take it to someone who can, so don't panic!
The backfire sounds like air getting in either on the inlet side (usually mounting rubbers, sometimes a loose hose on a vacuum connection or similar (I don't know what the system is on your bike) or exhaust side. Check these before looking elsewhere.
Tall men see everyone else's bald patch but their own.......