How long have people seen Flow Simulation work at Mesh Capturing and actually come back to life?

I've got a pretty intense thermal/flow model that is about 2.2M cells in the current mesh settings.  It has been meshing for 14+ hours overnight - most of that time with status: mesh capturing.  I know it's not a hard limit because I've made 6M cell meshes before (although never stupid enough to actually let it attempt to solve them).

I've never seen it come back to life if it gets stuck here for over an hour.  Anyone else?

My issue is: it's not completely in the weeds, the computer is still responsive.  How can you definitively tell when SW is dead and when it's deep in thought?  I'd hate to reboot only to have the same issue again and again.