Let's make a list of dead and depowered (or presumed to be depowered) mutants (I am considering both Logan and Xavier as Fantomex-Xavier as living characters)
A few rules
-We must know their names
-They must have appeared at least in 4 issues
-Only earth 616 resident characters
First 2 big groups of dead characters
-The original Hellions except Empath, Warpath and Firestar (those 3 are alive).
That would be Catseye, Roulette, Bevatron, Beef, Jetstream, they were all killed by Trevor Fitzroy. Tarot appeared alive last year in Spiderman/Deadpool 11 but I am not sure it's canon. She was acting very out of character, as a D list Spiderman Villain (think someone like Panda Mania), a Cards based thief, and the issue was written by Penn from Penn & Teller.
-The members of Milligan's X-Force and X-Statix except Doop, and perhaps Dead Girl, who had a mini with Dr Strange after X-Statix in which she resurrected (but I am not sure it's canon).
That would be U Go Girl, the Iconoclast, The Orphan, Vivisector, Phat, and many many others (all of whom died in action).
now normal list
Adrienne Frost (shot by Emma)
Alchemy (Terrigen mist poisoning while trying to destroy one of the terrigen mist clouds)
Avalanche (lobotomized by the Red Skull, had to be put down)
Changeling (killed by Grotesk while impersonating Xavier)
Christopher Bradley-Maverick (explosion)
Cyclops (Killed by Terrigen Mist poisoning caused by Black Bolt and Maximus)
Destiny (by Legion under the influence of the Shadow King)
Diamond Lil (Killed by Mortis)
Feral (killed by Sabretooth)
Garrison Kane (heroic suicide to save team from a brainwashed Madison Jeffries)
Harry Leland (killed of heart attack while fighting Nimrod)
Icarus (killed by Stryker, perhaps Nimrod too)
Jesse Bedlam (crucified by Church of Humanity)
Kwannon (legacy virus)
Lionel Jeffries (killed by Madison Jeffries)
Mastermind (legacy virus)
Madrox the Multiple Man (Killed by Terrigen Mist poisoning caused by Black Bolt and Maximus)
Maggot (killed by Sinister in the Weapon X Neverland concentration camp)
Moira McTaggert (Killed by Mystique)
Pyro (Legacy virus)
Risque (Sublime's U-Men)
Shard (heroic suicide to help Bishop kill Fitzroy)
Shinobi Shaw (killed by Sebastian off panel)
Skin (Crucified by Church of Humanity)
Sunpyre (Killed by Mystique)
Synch (killed by Adrienne Frost)
Tier (killed by Strong Guy)
Thunderbird (plane crash while trying to kill Count Nefaria)
Vulcan (killed by Black Bolt, like Scott)
Washout (an X-Statix original character that had over 10 appearances in Tieri's Weapon X, killed from the enhancements Wepon X performed on him)
Wild Child (killed by Omega Red)
Depowered
Abyss-Nils Styger (Nightcrawler's half brother, son of Azazel, and a horseman in 1995 AoA)
Adrian and Jared Corbo, Alpha flight members, probably the sons of Unus the Untouchable and brothers of Unuscione
Aero, a Guthrie like Cannonball and Husk and Icarus
Angel Dust, iirc, the super strong woman of the Deadpool film was her
Angel from Morrison X-Men
Artie
Beak, also, all their kids except the one they called Tito
Dani Moonstar
Fatale
Freakshow
Harpoon, a marauder
Jubilee
King Bedlam, brother of Jesse
Kiwi Black, half brother of Nightcrawler like Abyss, son of Azazel
Maverick-Christoph Nord
Phantasia (she had to receive mental treatment because she still had memories of the House of M reality)
Prodigy
Reaper
Scanner, an Acolyte
Shola Inkose
Slipstream, brother of lifeguard
Wicked
Wind Dancer-Sofia Mantega
Windshear from Alpha Flight
Presumed to be depowered
Cordelia Frost (we never even knew what her mutant power was)
Dr Knapp-Manikin of Alpha Flight, he hasnt appeared in comics since 1994 when Alpha Flight disbanded
Goblyn from Alpha Flight and her sister Laura Dean
Shortpack
The St Croix twins who were Monet most of Gen X (havent been seen since the 90s)
I have come to realize the Monets may have been inspired by Goblyn from Alpha Flight. 2 black female twins, who fused as one being, were considered to be only one being for a long time, one autistic, and the autistic one could open interdimensional portals. Goblyn wasnt that different from Penance in powerset and behaviour.
And Lobdell who wrote Gen X later knew that because he an Alpha Flight writer before.
please add any you remember and mention which ones you'd like to see resurrected or repowered
edit: Copycat is alive, she appears in the issue in which Deadpool marries his underworld monster wife he eventually divorced, Copycat still has her powers and works in a chimichanga food trick.
Diamond Lil was killed by Mortis, not Slene