The present behavior on normal 32-bit and 64-bit platforms is that, on both, 'int' is 4 bytes, and 'long long' is 8 bytes; and on 64-bit, whether 'long' is 4 or 8 bytes depends on the ABI/target OS.
I'd imagine it's quite likely that 'int' stays 4 bytes even on hypothetical 128-bit CPUs - there's not much reason to change it, as on 64-bit it's already less than the CPU width, and thus is pretty much arbitrary even today. But yes, anything that wants a 4-byte/32-bit integer should just use <stdint.h>'s int32_t.
I'd imagine it's quite likely that 'int' stays 4 bytes even on hypothetical 128-bit CPUs - there's not much reason to change it, as on 64-bit it's already less than the CPU width, and thus is pretty much arbitrary even today. But yes, anything that wants a 4-byte/32-bit integer should just use <stdint.h>'s int32_t.