It's probably fair to say that it stopped being a Crusader State a long time ago, but there is a continuity. The Teutonic Order created a state in the Baltic, which became Germany. I'd also suggest that maybe this is also already true. Then you have further afield - West Africa? Arabia? Mesopotamia? Africa? Spain? Good calls for Crusades there. With those three solidly under Christian rule, you have more options. It serves all three to keep the other two alive for political reasons (Jerusalem is a good buffer, and relies on their neighbours to prevent either of them dominating Jerusalem themselves). With Egypt to Anatolia under Roman, Jerusalem, or Egyptian rule, you'd be able to have either Jerusalem, Egypt or both surviving as the Romans still have their own problems and aren't guaranteed to take them themselves, as they have their own significant problems.
This then means a significantly good chance of taking Egypt, which has the economic power to establish a huge supply of Catholic mercenaries and other resources a state needs, that Jerusalem just does not have (and also secures that border). So I'd add a second PoD - the Fourth Crusade leads to a Papal bull that has Venice agree to a peace with the Romans and the return of some of their territories, and in return the Romans agree to join in, on land and sea, providing a much larger force for the invasion than the Fourth Crusade alone would have been. This could butterfly the events of the Fourth Crusade (perhaps saving Zara, or hurting Venice).
How does this allow the Crusader States to survive? A Stronger Byzantines means that they can play a hand in the Fourth Crusade from the initial pronouncements. This allows either the institution of a Co-Emperor to carry on the legacy of Manuel I (who was interested in conquering Egypt) or the future preparation of Alexios II to serve as a suitable heir. Personally, I think the best option is to delay the death of Manuel I by 10 years.
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