One of the expat Brits I know is very big on the idea of the EP election as a proxy for a second referendum. I can't really follow the logic. EP elections usually have relatively low participation and if there is a depressed turnout from people who think that, or want that Brexit happens I can readily see very middling results.

As to the results: I wouldn't expect anything drastic. I assume the Tories will lose some support since their whole strategy of absorbing UKIP is on fire. How much the TIGllers will cut into Labour's support I couldn't guess. From where I'm sitting they are too blatantly an anti-Corbyn outfit to run as a single issue anti-Brexit party.