Heav'n's not a neologism.
Or'll sings more naturally than heav'n.
Or'll's a bit ugly. 'Will' sounds better and conveys the meaning if you think about it for a moment.
When you sing it, it sounds just like 'all'. If I was writing a radio song (i.e., one that people just listened to) I think I'd get away with it. I'll admit that or'll looks ugly.