Gearbox Diff on its way out, how long will it last?

[CrookedSheep]

my astra is starting to rumble over the past few weeks and has been getting worse. i have had a few opinions and each garage has said gearbox diff.

before I splash out on a recon box, is there any telling how long the gearbox will last? i appreciate thats like asking how long a piece of string is, but i am wondering.

i am tempted to keep driving it till it brakes, unless someone can tell me why this is a bad idea.