I think Vermaelen was good when he played too. If he had been less injured he could perhaps have pushed for a starting spot. He didn't get an easy ride when he did feature but he handled it well.
I'm not opposed to him moving on as such, but it becomes one more hole we need to plug in the squad this summer. We only have one goalkeeper, no rightback who's fit to start, we're missing at least one central defender with Vermaelen in the squad, we're entering our 4th season without a good backup for Arteta and (if we're serious about improving the team and not just maintaining status quo) we could still use a leftback who's less injury prone and more accomplished than the ones we've got. These are things that cost time and money to sort out, and we have to do it in addition to the two or three top signings we desperately need if we're serious about next season. It's just too much work for one summer.