I assume you're talking about mobile, and a 3D game. If either of these is untrue, you should be perfectly fine in any situation.
I'm currently working on a 3D tile-based mobile game. I've written my own tile engine for Unity (note: I didn't write my own renderer, I honestly don't see the point). In the game the camera rotation is fixed and it's ortographic, which allows some optimizations.
While having a 200x200 map is easily possible (and has been done) with my system, older phones like my Samsung Galaxy S are simply too slow to use it, even after optimizations. Fps can be between 5 and 20 which means it's not enjoyable.
One important thing I noticed is that after optimizing graphics a lot (custom static batching, throwing away invisible sides, generating a custom terrain mesh, etc.) the choke point wasn't really graphics. Since with isometric games you have a pretty good idea of what the player sees at each point, it's very easy to minimize the amount of data that needs to be loaded.
So right now the weakest link is the amount of units and non-static stuff on the map.
Pathfinding is acceptable with a pre-calculated graph (using A* from Aaron Granberg). For collisions I use an optimized model with boxes spanning multiple tiles (pre-calculated) and unity's physics engine, but I don't do any dynamic body stuff, only checking for collisions in certain situations (player movement mostly).
So the final answer is: yes. You may have to cut back on the features, but it is definitely possible.