Absolutely not. The only criteria for selling should be whether he wants to go. And, sorry, while many on here might disagree, you can't have it both ways. You can't claim to be a Celtic fan and know exactly what it means to win 9 and 10 in a row to the fans and then say 'but Arsenal were offering me lots of money'. Arsenal aren't a top club in England anymore. It's not like they're challenging for the title or the CL (obviously not even in that). Not even close to any of those two. So going to Arsenal cuz they can give you 80 grand-a-week is just mercenary stuff. Call me self-righteous or whatever, but if that's your attitude, you ought to just stop with all 'I love Celtic' stuff and admit straight up that you just want to have lots and lots of money. Fine. That's the way of the world 99% of time; hence why the world is such a horrific place.
I'd even understand more if it was Man Utd, as they are, regardless of their current status, the biggest club on earth. There's a romance involved in Man Utd and they have the prospect of once again challenging for the title and taking on Europe. I don't see that at Arsenal.
I must say here that all of the above is hypothetical. I don't know KT's mind on this. I hope he stays and if he leaves for Arsenal in the above context, while I would never wish ill on him, I will certainly think less of him.