Corner Cases - Banishment vs Plane Shift

How would you rule the interaction between Banishment and Plane Shift (or any other interplanar travel)?
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[@mandocomando9444]

Mayhaps the fiend makes the save against banishment again? If they are concentrating on banishing the fiend and it wriggles back through the hole it seems like they are still pushing against it so roll the charisma save for the fiend again. You could also rule it like counterspell where the higher level spell has priority, so 7th level plane shift cancels 4th level banishment. Or then again, just plane shift after the fight and not have the problem.

[@cadenceclearwater4340]

The evil demon will accept the banishment, then after the time elapses, and they planeshift back, they're simply waiting behind the next door the party opens.
Boo!!!

[@scatterbug]

I just shout "Go home! You're not my friend! Nobody likes you anyways!" And hope they get sad and leave.

[@PVS3]

Banishment is 4th level. If your opponent burns a 7th level spell to undo it's effects then the spell effectively ends but you still get value. You're just concentrating pointlessly, like when you ponder if the weave looks more like crochet or knitting.
There are other concentration spells where whatever effect your holding becomes moot. Hold Person and Slow don't say the spell ends if the target dies, but you'll see no difference if they did. Same here - they return to the.. oh, they're already here.
Another angle: I can burn a spell slot to plane shift to the same plane (ping 127.0.0.1) and just go nowhere. That's what's happening when you drop your concentration on banishment in this niche example.

[@RulesandRulings]

The RAW version of events is probably fine. Trading out a 4th for a 7th level slot is pretty good, assuming your DM is running their enemies with actual resources to burn. Interesting to think about, anyway.