There are always those X-men taking short breaks from the X-men books, but for some the breaks never last very long.
Bishop and Archangel recently shined again in Astonishing and it's just a matter of time to see them return on a soon to be (re)launched X-Men series.
Rogue and Gambit recently returned in Astonishing, Gold and will have their own book later this year.
But you also have those who were members for quite a while, but have not been on any active rooster for a few years. Some seem totally forgotten (Madison Jeffies, Doc Nemesis, Marrow) and some just serve as cameo stars for one or e few issues (Magma, Northstar, Cece, Hope) and some have been on other teams, but not on the X-Men (Cannonball, Sunspot).
Now which former X-men who have not been on any X-Men team for at least two years deserves to be back on an active team roster?
Some long time inactive X-men (to name a few)are;
Marrow
Cecelia Reyes
Shatterstar
Omega Sentinel
Dani Moonstar
Magma
Madison Jeffries
Karma
Hope Summers
Sunspot
Slipstream
Darwin
Sunfire
Vanisher
Cannonball
Doc Kavita Rao
T-Bird III
Doc Nemesis
Forge
Firestar
Lifeguard
Sage
Northstar
Warbird