#JavaScript (ES6), n=1
This was very difficult, and deserves a thorough explanation. Which I will write later, after I explore this challenge a little more!
etTimeout=stTimeout=seTimeout=setimeout=setTmeout=setTieout=setTimout=setTimeut=setTimeot=setTimeou=unescape=>42;
setTimeout
`c="function f(){x=String.fromCharCode(96);n=String.fromCharCode(10);q=String.fromCharCode(34);y='etTimeout=stTimeout=seTimeout=setimeout=setTmeout=setTieout=setTimout=setTimeut=setTimeot=setTimeou=unescape=>42;'+n;z='setTimeout'+n+x+'c='+q+f+';f();_=1'+q+';if(window._);else if(c.length>339)eval(c)//'+x+'///'+x+n+n;console.log(y+z+z)};f();_=1";if(window._);else if(c.length>339)eval(c)//`///`
setTimeout
`c="function f(){x=String.fromCharCode(96);n=String.fromCharCode(10);q=String.fromCharCode(34);y='etTimeout=stTimeout=seTimeout=setimeout=setTmeout=setTieout=setTimout=setTimeut=setTimeot=setTimeou=unescape=>42;'+n;z='setTimeout'+n+x+'c='+q+f+';f();_=1'+q+';if(window._);else if(c.length>339)eval(c)//'+x+'///'+x+n+n;console.log(y+z+z)};f();_=1";if(window._);else if(c.length>339)eval(c)//`///`
Basically, the first line is carefully constructed to rename all 'mispellings' of setTimeout to valid functions, so that if a character is removed from one of the setTimeouts the code will not error out and the unscathed version can run. It is also written so that if any one character is removed from the first line, there will be no error and the rest of the code can run unaffected.
The second and third blocks are exactly equivalent. If one runs to completion, it sets the _ variable so that the other knows not to duplicate the quine. If one of these blocks errors out, it does not affect the other block because it was called asynchronously using setTimeout. The error will cause _ not to be set, so the other block will quine successfully. The main code is in a string, which is checked for length in each block to make sure that there were no removals.
A better explanation is forthcoming. In the meantime feel free to ping me in chat @jrich with any comments/questions/criticisms!