Well, you can't very well go strongly after CM until you know for sure if Thorne is out. And don't know how one can say the odds of getting a quality to even serviceable 5th yr big is "none".
I grant that it's not easy to nab one, but every year there are solid options, and after taking a quick glance, you see guys like Shonn Miller (UConn), Anton Grady (Wichita St.) and Damion Lee (Louisville) were excellent bigs for their teams last season. Plus as others have pointed out, 5th yrs have done rather well here when healthy, so I think the sales pitch can be rather good - play in the B1G, upperclassmen roster, immediate playing time, could be missing piece, yada, yada, yada...
But if Groce opts to go hard after CM and that recruitment drags out, then he pretty much guarantees no additional post help for next season.