Even if the Hamas/PA negotiations are successful, and even if Hamas agrees in some symbolic way to avoid explicit support for terror attacks, and even if they manage to convince the EU and the UN that the combined entity is willing to adhere to existing PA commitments...
...there is still an easy way for terrorists to continue to attack Israel with impunity.
Today, Islamic Jihad announced that they will not take part in any potential "national unity" government. Similarly we have supposedly new organizations like Palestinian Hizbollah Brigades whose entire stated purpose is to continue terror when the more mainstream groups have public truces.
We have seen in the past that members freely go between the terror groups and that attacks are often jointly executed. Similarly, we have seen Palestinian Arab leaders pretend to be helpless when these "rogue" groups continue their attacks, as they aim to gain Western sympathy and aid while they can clandestinely support the all-important "resistance." Hamas might have had little patience for the Al Aqsa Brigades after their Gaza coup, but they are quite happy to allow Islamic Jihad to control many dunams of land in the densely-populated Strip purely for terror training.
It is an old playbook, and it is one we can expect to see again and again as long as gullible Westerners continue to believe their own wishful thinking more than the ugly facts.