The modern, euphemistic, transitive use can be found many times before the OED's 1979 citation, in Joseph Heller's 1961 novel Catch-22:
She had urgent news about Dunbar.
'They're going to disappear him,' she said.
Yossarian squinted at her uncomprehendingly. 'They're what?' he asked in surprise, and laughed uneasily. 'What does that mean?'
'I don't know. I heard them talking behind a door.'
'Who?'
'I don't know. I couldn't see them. I just heard them say they were going to disappear Dunbar.'
'Why are they going to disappear him?'
'I don't know.'
'It doesn't make sense. It isn't even good grammar. What the hell does it mean when they disappear somebody?'
'I don't know.'
Jesus, you're a great help!'
'Why are you picking on me?' Nurse Duckett protested with hurt feelings, and began sniffing back tears. 'I'm only trying to help. It isn't my fault they're going to disappear him, is it? I shouldn't even be telling you.'
And later on:
"What does Major Major say?"
"We never see Major Major. He seems to have disappeared."
"I wish we could disappear him!" Colonel Cathcart blurted out from the
corner peevishly. "The way they did that fellow Dunbar."
'Oh, there are plenty of other ways we can handle this one,' Colonel Korn assured him confidently, and continued to Piltchard and Wren, 'Let's begin with the kindest. Send him to Rome for a rest for a few days. Maybe this fellow's death really did hurt him a bit.'
And again:
'They'll probably try.'
'What did Major Major say?'
'Major Major's gone.'
'Did they disappear him?'
'I don't know.'
'What will you do if they decide to disappear you?'
'I'll try to stop them.'
And finally:
'No hope at all, is there?'
'No, no hope at all,' Major Danby conceded. He looked up after a while with a half-formed notion.
'Wouldn't it be nice if they could disappear us the way they disappeared the others and relieve us of all these crushing burdens?'
Yossarian said no.