Laiki Enotita (Popular Unity or People's Union) is the name of the new party that will fight for the most genuine Syriza vote. There are no opinion polls yet on how this new party may fare but it is clear that, judging on the June and July data, Syriza as a whole gathered more than 40% of popular support, twice or more what the conservative New Democracy has, and seven times what smaller parties can gather.
Within the former Syriza's bench in Parliament, they have at least 25 seats, being formally now the third largest party of Greece (displacing the much smaller nazi party to fourth position). Their presence withing the crumbling Syriza middle and low ranks is or was no doubt much stronger but Tsipras manipulated the party's institutions to delay decisions and now has forced elections before a congress can be elected and meet.
The enigma is how will the vote split in the snap elections of September: will most Syriza supporters back Tsipras for his alleged "charisma" and "doing the best he could" (so he claims) or will them demand a clear-cut anti-Troika program, much as they did in the July referendum?
My impression is that former Syriza voters may well be roughly evenly split, between the fearful, who will back Tsipras as "lesser evil" and the outraged, who will not want anymore of him, his lies and his betrayals. If this hunch is correct, then Tsipras will only be able to form government with the conservative New Democracy (and some lesser partners), intiating a four-year term of surely catastrophic third pro-Troika coalition cabinet, with very reinforced left-wing opposition (but opposition nevertheless).
A key issue will be which of the three contenders will get the first post, which, by grace of the Greek electoral law (otherwise very proportional), gets 50 extra seats (out of 350). However, unless Popular Unity manages to get most of former Syriza backers, it will be unable to form government and pro-Troika parties, now possibly led by Tsipras, will have to form a colorful coalition in order to lick their masters' boots properly.
As for Yanis Varoufakis nobody knows yet, not even himself possibly. He has repeatedly stated that he meant to be in politics for long but it is unclear if he will join (and be accepted) within the ranks of the new party (whose members probably feel he is way too moderate, even if respectable). He won't be included for sure in the Tsipras list because he broke the party's discipline. Clearly Varoufakis would be an asset for the new party in terms of attracting votes but it is not so clear if the Popular Unity program, which seems now persuaded of the need to evacuate the Eurozone and even the EU itself maybe may fit with the Europeanist feelings of the former Finance Minister.