Keeping or even buying an 'experienced head' is absolutely fine, remember Alex Manninger?
However, there lies a problem with this particular scenario and that is Milner is already on very high wages.
He's definitely worth having in the squad as a wise head, commands respect and leads by example but as a player I think the tank has run empty now.
If it were me, I'd let Milner go for a year or 2, finish up his career back at Leeds, then return as part of the coaching setup.