I'm not entirely sure how to ask this question since this spell starts bending reality in ways that are difficult for me to envision. To be fair, though, that's kind of the point.
This answer posits that the illusion created by the mirage arcane spell is not real and entirely superficial. I'm not sure, but it seems like this runs contrary to the notion that the spell creates tactile elements which makes me think that you could push off the illusion (which isn't unheard of for shadow illusions from 3.5).
The spell's range is "sight" and it can affect "terrain in an area up to 1 square mile", which depending how you shape it, can be incredibly long. Were I to only make it 10' wide, I could run that out for 528 miles (assuming I could see that far away).
- Ignoring the feasibility of seeing that far, could a Wizard use this spell to create the illusion of a smooth path across a stretch of raging ocean to permit the party to walk overland between continents?
- Do the party members who believe the illusion walk upon the strip of land, enjoying the safety of the land? If so, do they move slower than they think they should? Assume none of them have a swim speed.
- Or do they fall through the illusion and start drowning? Do they even realize they are drowning? If so, when would they realize that?