The media, hollywood and the ruling class hate him with a passion. Not conceding, ever, cost's him nothing at this point. So the fact that he hasn't conceded, really doesn't mean anything.
As for what, dwindling, options are left. Forget about the fed congress. Sure, there will be a rep, and possibly a senator contesting the elector votes. But that's exactly as far as that will go. There is zero percent chance, Pelosi's House will vote in favor to drop several biden votes. At that point, it doesn't matter what the senate does or doesn't do. That avenue, is closed.
There really are only two exceedingly impossible situations left that will keep Trump in office:
1. The republican legislatures in the contested states, finally exert their Article II Constitutional authority, send a different slate of elector votes (or non at all) to their Governors to send to the Congressional Archivist by January 3rd, 2021.
2. The military steps in and prevents biden from being "sworn in."
I have zero faith that the republican legislatures in question will exert their constitutional authority.
As for the military option...
Military tribunal sounds like the perfect option. The real winner, Trump, stays in office and we round up all the criminals.