Same as Donny, there, Ian... I got my songs backed up to audio, and would use another keyboard.
Until Yamaha come out with another (hopefully lighter!) 76 note arranger, this point has always been kind of moot with us, anyway. My needs MUST have a 76-er (it's integral to the way I play). You give 2 1/2 octaves to a bass split on a 61-er, that's only 2 1/2 octaves left for the RH. Pretty slim. Do it on a 76-er, you still got 3 1/2 left. MUCH more usable.
Some people (especially those not playing full piano parts on a regular basis) can make do with less. I can't. When Yamaha come out with another 76, we''ll talk again...
And I though we were done with biting each other's heads off for the slightest thing... If I thought you were being dishonest, Ian (which I don't), I would simply say that. It's an expression, for Chris' sake!
And you are right... Some pro's DO have a spare duplicate of their main axe. But many, many, many more DON'T.... They've got other keyboards, even other arrangers, sometimes. But short of major touring pros (and the tour often provides the backup), I think I can be reasonably confident in saying the large majority don't. Remember (before you get your dander up again

), I am not saying that NONE do, I am simply saying the large majority don't.
Do you disagree with this? (And I won't accuse you of calling me a liar if you do!)