What if come May 18, Muhyiddin loses the vote of no confidence in Parliament? Most likely he will ask the King to dissolve Parliament and that will lead to a snap election.
If that were to happen, Pakatan Harapan needs to work out seat allocations among DAP, PKR and Amanah to cover practically the whole of Malaysia, including seats contested by the Dr M faction of Bersatu and Warisan.
The reason is obvious. PH needs to be able to form the government without relying on parties outside of the coalition.
Warisan has been with PH all along but don't forget, it was originally supposed to be part of the Sheraton Move. So far, its leader Shafie Apdal has declared support for Dr M but not necessarily for PH per se and not for Anwar either. So wherever Dr M goes, Warisan is likely to go too.
Dr M's faction in Bersatu is only around six people at the moment. But in the close fight for control of Parliament, six seats can make a huge difference. If majority control depends on those six seats you can be sure Dr M and gang will want to assert control over PH and call all the shots. And if they don't get their way, they are likely to pull Warisan with them too.
So, PH must be prepared to contest not only in constituencies where Muhyiddin's Bersatu, UMNO/BN, PAS and GPS are contesting but also where Dr M's faction and Warisan are contesting.
They could make a deal with Dr M and Warisan to be friendly parties and avoid contesting in the same area but they should require Dr M and Warisan to publicly (and loudly and frequently) assert their allegiance to the PH cause, saying if they win their seats they will support a PH government.
This is not a surefire guarantee that they won't just turn around and team up with some other faction to set up some new rival coalition but it would make their name be mud in the eyes of the public if they do so after persistently and very clearly telling the voters their allegiance is with PH.
That is one approach if they want to go into the election with Dr M's faction and Warisan as allies. It's probably not the best option though. It's much better if PH goes into GE15 alone, meaning the three parties in the coalition go for a majority on their own.
Whereas in GE14 they needed Dr M to create the tipping point for the tide to go PH's way, in GE15 the situation is very different. Dr M may be a master politician but after the Sheraton Move and Unity Government debacles, he's pretty much a spent force. They can and should try to win GE15 without him (or Warisan).
If they win, even by the slimmest of margins (let's say 112), you can be sure there will be a lot of MPs and parties knocking on their doors asking for cooperation and collaboration. They can accept these MPs and parties as friends of PH outside of the coalition. But they should never make the same mistake as they did before in taking in a party like Bersatu, which never fit well with the rest of PH, and then allow this relatively small party take over the reigns of the coalition.