Agree. Only said with tongue in cheek!
Wouldn't be surprised, only time will tell. With the collapse of the proposed enhanced timetable way back just after SWR took over, the need for the additional fleet (442 originally, and 458 subsequently to replace former in theory) evaporated. As has been pointed out countless times, the (electric) service timetable that existed at the point of handover from SWT to SWR could be managed today/future with 701's and Desiro's alone in their proposed/present (respective) numbers.
My belief, based on gut feeling alone, is that the 458's in their new guise will remain until the full 701 rollout is in place, and then a decision will be made on their future. In crew knowledge (hence also rostering), and spare component terms, they are far less flexible than the Desiro fleet or the 701 (as proposed).
The rebuild from 5 back to 4 car format was (I presume?) designed around the theory of them being allocated to the PDL to replace the failed 442 plan, and the old 2+2 v 2+3 seating arrangement (on 1Pxx only it must be stressed) and so very likely the contracts for that work at Widnes were all in place etc, and so the work went ahead, despite things having changed on the ground by then (dropping of the enhanced TT plans) - if politics and ensuring promised employment went ahead as planned, came in to this equation, who knows?
Obviously they (4 car 458s) have come in handy to keep things moving whilst the 701 issues are resolved.