Welp, Turkey only needs the F-35 for
three particular reasons:
- NATO interoperability: The F-16s will eventually have to be retired and, even with a comprehensive MLU, they won't remain competitive into the 2030s. What modern aircraft fulfills NATO interoperability requirements better than the F-35?
- Nuclear sharing: Same reason. The F-16s will have to be retired by ~2040, and Turkey will eventually need a replacement. Kaan won't be certified to carry B61s.
- Test & Evaluation: Kaan won't reach IOC immediately, the earliest deliveries won't even begin until 2029 and its initial focus will primarily be A2A. There are six Turkish F-35s already in storage that could be delivered soon (in about two years), and this is where they come in. Incidentally, countries that pose a threat to Turkey are also in the F-35 club, so another benefit is gaining first-hand experience with the platform and preparing accordingly.
Turkey is a major UAV powerhouse, whose first LO platforms are set to enter service this year, but that experience still won't come anywhere close to operating a manned LO deep-strike fleet built around a mature design. Supplementing those six already-built aircraft with new orders won't result in additional deliveries before at least 2032, but they would still provide highly valuable operational experience.
As such, there's a reason why the military is only interested in around 40 aircraft at most --most of the planned ~500-strong combat fleet will be made up of indigenous aircraft, and you simply don't need any more than 40 F-35s for those three reasons.
I don't think re-admission into the programme is possible. All Turkish workshare (except for the engine parts) has already been redistributed to other partner nations or new customers, most notably Germany. Rejoining would also require the approval of all partner nations, which certainly won't be easy... Still... you never know.