The main change within Hamas's internal system following Sinwar's elimination is the shift of Hamas's center of gravity to Qatar. This means heavy pressure on Qatar to activate the deal, but Qatar won't willingly comply because of the United States' intention to establish a Saudi Arabia-Israel axis, which Qatar won't agree to. Regardless of who is officially chosen, the strong man of Hamas is Khaled Mashal, a man of trust and Qatar's agent in the Arab sphere. If Dahlan is the UAE's man, Mashal is Qatar's man. Syria and Iran have vetoed him due to his betrayal of Assad, but in practice, he's the closest to the Emir's court and the real decision-maker.
With the balance tipping towards Qatar, it's less important who will lead Gaza, if anyone. Mohammed Sinwar is the senior Hamas figure in Gaza, but Gaza's overall importance has plummeted.
I know from Egyptian sources that they've had their eye on Khalil Hayya for a long time, as they monitored the reconciliation talks between Fatah and Hamas in Cairo. He was very dominant, and I estimate they might mark him as the one to replace Sinwar as someone they can rely on after Sinwar. However, all this depends on whether Israel opens the Rafah crossing. As long as the crossing is closed, all the influence of Egypt is blocked along with the UAE, Saudi Arabia, and Indonesia, which showed interest to enter Gaza but was rejected.
Abu Marzouk is suspected by his colleagues of having connections with the United States, and therefore he doesn't sit in Qatar but in Amman. He's acceptable to Egypt, but the fact that he was Secretary-General and is no longer indicates that he's not highly regarded by Qatar and the Muslim Brotherhood in general.
פנחס ענברי - מזרח תיכון מסובך במילים פשוטות 