A promised appointment?

[neb090]

John, Chris, and Tom have been very good friends since their childhood. And when they were children, they often played under a 50-year-old banyan and they have lots of good memories there. Now, they all grew up, and John plans to move to another country, so Chris and Tom went to the airport to see John off and they three promise one day they will again go to see the banyan and talk about their lives.

So should I say "It is their promised appointment?"

Is it possible to use "It is their something." to write this sentence?

(For example, "It is their shared memory.")

 

[5jj]

John, Chris, and Tom have been very good friends since (their) childhood. And when they were children, they often played under a 50-year-old banyan and they have lots of good memories there. Now, they have all grown up, and John plans to move to another country, so Chris and Tom go to the airport to see John off and they three promise one day they will again go to see the banyan and talk about their lives.

 

[teechar]

So should I say "It is their promised appointment?"

No. For a start, "appointment" is too formal and implies a specific time/date.
Consider "It's/that's what they promised they'd do".

Is it possible to use "It is their something." to write this sentence?
(For example, "It is their shared memory.")

It depends on the context.

 

[tedmc]

How about "they desire/hope to meet one day to relive their childhood memories"? There are also "to revisit a place of nostalgia" and "taking a walk/trip down memory lane".