The Constitution requires a majority of senators (51) for a quorum. Often, fewer senators are actually present on the floor, but the Senate presumes that a quorum is present unless the contrary is shown by a roll call vote or quorum call.

However, at least 1 Democrat has to be present to issue the quorum call. In the absence of a quorum call, quorum is presumed to have been established.

...to compel their presence ?

Wisconsin did this and they issued a warrant to be carried out by the Wisconsin State Police. Everyone went to Minneapolis so they were out of jurisdiction. Probably harder here - everyone have to go to Canada, eh ?

Not sure if it applies to the feds but it was a fun couple weeks watching the games in Wisconsin.

Flake? Corker? Graham? Anyone?

maybe if it was something that was directly about Trump... but not for this.

If McCain dies or resigns, the Governor of Az can replace him and it must be with a Republican
https://www.azcentral.com/story/news/politics/arizona/2017/07/20/what-if-senator-mccain-leaves-office-how-process-works/494621001/

or would she decide her best chance is to win this fall and replace Flake and serve for 6 years?

and show us one more of those patented thumbs down calls. Along with a solidarity/farewell vote from Sen. Collins, that should do it.

Yeah I know, don't hold my breath.

except for a trip to the bathroom... maybe

Nobody wants to pass in a hospital, or worse yet, a hospital away from home. Fly him up, wheel him in for the vote, fly him back. It's a long shot, I know. He may only have days or a week or two.

Our son was in the ER, for what turned out to be a relatively minor thing, the night he gave his famous thumbs down. I won't ever forget everyone watching that vote on TV, while simultaneously attending our boy.

but I don't think he survives a trip to DC.

I just heard that his long time aides and friends are gathering in AZ (flying there today). My guess is that death is within hours or days at most.