I've said it before, there's plenty of evidence that the Potara just does not scale up to Blue levels of power, the fusion ended very quickly.

It may be due to the perfect Ki control Blue has, but, the dance seems to properly scale to Blue. It makes sense, those earrings were created for beings much weaker than God level Saiyans and not even designed for Saiyan biology, where as the dance seems to be designed for anyone who can do the dance, have similar size and can control their ki, it's not an "item" it's a technique, it's power comes from the users.

All else being said, on screen fears, even though people are gonna come argue that "we don't really know how long Gogeta fought Broly" Vegito loses the fight due to his fusion ending.

Using your no time limit rules though, the fight ends in a draw. The Potara wouldn't give a big enough difference in power to change the outcome.