Never, or we've already had 1024 bit cpus, where have you been?
There have been VLIW (very long instruction word) cpus, but they haven't worked out that great (the Transmeta cpus were, for instance). VLIW would be the 1024 bit.
Never as 64 bits ought to be enough for longer than we can make sane guesses. Now for file systems, that's another matter, as Sun figured that 64bits would be hit in a decade or two (a decade from now) so they made ZFS 128 bit, so it should be good until it is obsolete for other reasons.
The last thing is you are just talking about instruction width, there is addressing and data. So to stick with the PC, the first PC had a 8 bit data bus, but a 20 bit address bus. From the Pentium Pro on, they have ahd the ability to do 36 bit addressing, and the various sorts of SIMD allow for data at 64-128 bits.
Itanium (ia64) is 128 bit, but that is really 3 40 bit instructions bundled together.
And with IPv6 (128 bit addresses) I can see specialized router cpus being more than just 128 bit for data, but who knows?
