It is kinda ironic that the Hamas attack is only 1 day after October 6th which is the day in which the Egyptian army managed to cross and break the so-called impregnable Israeli defences and liberate Sinai penninsula in 1973 as far as I remember
Hamas planned a lot for this attack, that much is clear. Though, there is a 80% possibility that they will lose in the end since the Israeli Armed forces arent that weak
Lose in a sense of loss of land, probably. But, the absorption of Gaza back to Israel meant that there would be no clear line between the Palestinian and Israeli. No longer you have a clear concrete line, you now have an imaginary line.
In the case of Afghanistan in 2001, the loss of Kabul didn't mean the collapse of fighting by the Taliban, it merely transformed from a fighting with a clear frontline into a war of attrition with an imaginary line. Recently it si also demostrated that the loss of Raqqa and Mosul doesn't stop ISIS from fighting either. They merely adapt.
So HAMAS should've planned for this kind of contingency. What if Gaza is no longer able to be defended ? Should they build operational bases for urban guerillas deep inside Israel, retreat to the Sinai ? or even establish bases in the desert of Jordan and S.Arabia. That will be up to the HAMAS, but then again guerilla groups are proven capable of executing the damage needed to keep the war in flame for a very long time.
Just like how 20 years in Afghanistan is enough for the world's geopolitics to change considerably back to the Taliban, HAMAS needs to plan for a long war until the geopolitical situation in the world reverses to their benefit.