Heaven 17's Martyn Ware revealed for the first time on his Electronically Yours podcast that Ian Craig Marsh had issues with mental health over time, then literally disappeared from the band never to be heard of again in the late 90s.
The comment centered around the failed 1988 album Teddy Bear, Duke & Psycho, & the nicknames given to the band by Terence Trent D'Arby when the produced his Introducing the Hardline According To... album a couple of years before. Psycho was Marsh. Ware made an apology for the misguided nickname.
Rumours were Marsh went into teaching on the south coast, but have never been substantiated.
Heaven 17 recently played the first 2 Human League pre-Dare albums Reproduction & Travelogue in full recently during 1 off shows in Sheffield & London, with Marsh, Oakey & Wright being thanked heavily for what they produced. Hope was Marsh might re-surface, but it wasn't to be,