Cutting back grape vines

[Rivian]

I have one running along above my bonsai benches and want to clean out the area.
It was hit with fungus this year and has lost most of its leaves though it may still be growing weakly at the tips.
Think I can cut it back heavily and defoliate now or will that cause it to flush out again this year?

 

[Starfox]

If trees still have there leaves on it'll likely flush out again, especially if you have some warm days left but that may not be a bad thing so it can gain a bit of health back before winter.

Generally heavy pruning back to two buds is done in winter when the vines are dormant but it's not really a problem to do it now. You just may have to do it again later is all.