Here's a few reasons to keep him.
I think he was fit for pretty much most of last season.
He counts as a home grown player.
He's only 28.
Makes business sense to have him on a contract and sell on if it doesn't work out than let him go for free and pay a premium for a home grown squad filler.
Any player who isn't coming close to retirement deserves a chance under the new management.
Having Gibson at the club could be another reason for Rooney to switch from united. (1)
He was Evertons best player when Koeman last saw us a few months ago.
He has experience of winning the premier league. (2)
Here's a few reasons to let him go.
Poor fitness.
Poor off field behavior
(3, 4, 5 & 6)
I think it make sense to keep him, at least till Koeman has had a chance to assess him properly.
1 - Interested to know how you think DG could influence Rooney to return ?
2 - That was over five years ago, when he was a slightly better than average footballer in a very good team. The Premiership has moved on considerably from those days and he hasn't, in real terms he has gone backwards.
3 - not a ball-winning tackler, a trait widely thought to be beneficial in a midfielder.
4 - no pace about him whatsoever, another trait useful in a midfielder. He could get away with that as a squad player at Manure over five years ago - not in the Premiership of today.
5 - Not very good in the air.
6 - Despite having a reasonable shot, doesn't get forward enough to put it to good effect and that's probably because he knows in himself that he hasn't got the pace to recover ground if/when the opposition break quickly.
He simply isn't good enough in my opinion to warrant this contract extension.
That said, I hope for his and our sake that he has got himself fit, stays fit and if/when he plays, he somehow raises his level of application and performance to heights never yet reached by him.