Terminal .write() stops working after component is first unmounted

[xobs]

Description

When a component is unmounted, XTerm.tsx calls this.terminal.dispose(). As part of this call, xterm.js sets _isDisposed = true and destroys its .write() call.

Thereafter, all calls to .write() will silently fail.

I have an issue open at xtermjs/xterm.js#3939 to address this, but I suspect this may be the wrong approach to take to unhook key handlers.