The 60+ F-5 are totally obsolete and will be scrapped soon. I don't see Taiwan Air Force accepting such a large decrease in airframe numbers when Beijing is buying more and more advanced fighters.
Well if the US Congress only approved for upgrading existing F-16, but the upgrade packages still provide those F-16 eq capability with the latest F-16 batches, plus the existing Mirage 2000 still performing well then Taiwan perhaps should reopen IDF Ching-Kuo manufacturing line. Afterall. IDF itself was designed as F-5 replacement.
I know it's not perfect. But considering the situation, what else Taiwan can do. At this moment the existing supplier won't provide new airplanes but only agree to heavily upgraded the existing ones (got some old remarks that even French still open to discuss upgrading existing Mirage 2000). Even potential there's additional Mirage 60 2000-9 in market soon (ex UAE), if the deal reached between French and UAE to resale them back to French as part of Rafale deal. However if US won't add new airframe, and what chances the French will also add new airframes.
Perhaps under circumstances, Taiwan should considered finding new packages for ('say') IDF NG. I think given new smaller AESA coming to market, and better electronics plus composite material available in the market, Taiwan can create suitable IDF NG that can closely match latest F-16, let alone latest J-10.