I recently had timing belt and water pump done because of leaking balancer seal. When I got car back I noticed .25 inch gap between block and cover. I can see belt spinning through gap. He must have forgotten to put in lower seal I think. This seal is very important right? Can crap get in there and damage belts? Should I insist on him fixing this?

 

there shouldn't be a gap like that with or without that seal being there. You should take it in and have him fix it.

and yes, it is possible for something to get up in there and tear up the belts.