Can ruined whipped cream be rescued?
I don't think so. In the mayonnaise case, all that has happened is the fat has come out of emulsion and gathered together again, so you can re-emulsify it. In the whipped cream case, you've started to create large fat crystals (butter). I guess technically it might work to heat it up to melt the butter, re-emulsify it into cream and then beat it again, but I don't think it would be worth the effort. You could go ahead and finish churning it into butter and buttermilk if you want to avoid wasting the cream.