I don't think you want any 'tweeners' as starters. Glover will be unhappy if he isn't starting. And making a transition to a 3-4 might take Glover more than 1 season to make. I'm not sure the Cowboys want to invest that time into an experiment.
Not with a guy like Glover who can start on anybodies DL in the NFL in a 4-3.
He's going to be shopped to somebody who can use him in a 4-3 defense and a 50+ play guy..
BP made several statements during his interview at the Combine to the fact that he's available as is anybody on the defense for the right price. Since BP doesn't make a bunch of false statements, I'd take that as clear speaking made so other teams will hear it and ask questions.
I think there will be multiple teams interested in the guy who is coming off another Pro Bowl year and isn't too old. I wouldn't doubt that the HC's there were all talking about who might be available for trade after FA has begun.
If he stays, he probably won't start. And to not have him be a starter would be a crime. It would be a waste of a year for him and devalue him to keep him for another year. Trade him now while he has value to rebuild the defense.
They will draft or sign a DE for their 3-4 to go along with Fergusion and they will need a draft pick or FA player who can play OLB in the scheme. Most teams would do one or the other that is losing some DL players in FA now.
Right now is the time to shop him, while teams are going to be looking to fill holes and aren't going to want to wait for the draft and take unproven players.
Glover is a proven player. And there are plenty of 4-3 teams that need to improve their Dl's.
In our new schemes, we need about 2-3 stud LB's. Glover should secure one of those for us.
Now, about Ellis..? He might take a bit longer to shop as he's not the name that Glover is. But some teams will pay for him being a former #1 and being very productive and versatile in a 4-3 playing either end and even can play a little DT.
I think he's gone, too. Same way. We need the players to remake the "D".