Yes, SV and AI have an interline agreement, so they can check your bags to KTM. You need to check in and collect boarding passes at Air India's transfer desk in DEL.

You cannot count on SG agents transferring your bags - indeed, you shouldn't count on AI agents to do it either. If you want to fly to KTM via DEL, you should get an Indian transit visa. If your SV flight is delayed, you'll be stuck airside and you may be deported if you do not have a valid Indian transit visa. If flying SG (or AI without interlined bags), I would expect to pick up bags and recheck them, and only consider help from the airline to be a bonus.