They will send gate and ramp agents from SEA on the rescue flight to assist with the pax / bags transfer. But, RE: bags, it really depends on what equipment the base has at their disposal. Since bags on widebody A/C must be in containers, if they don't have a container loader on hand, the checked bags will probably have to sit there until the broke airplane is fixed and ferries out. A narrow-body A/C that diverts would not have this issue, since those bags are bulk-loaded and aren't in containers.

I believe Cold Bay, AK still has a Delta de-ice truck there from a previous ETOPS diversion, it was cheaper to just write it off and leave it there rather than package it up and send it back somewhere in Delta's network. So you never know what sort of oddities are lying around some of these remote ETOPS fields.