Intel already has TSMC 7nm equivalent process, it is called 10nm++. Intel's 7nm is also supposed to be roughly equivalent to TSMC 5nm so as long as Intel can figure it out in time, it will have 5nm covered in-house too.Just think about if Intel went to TMSC and used their 5nm.
Meanwhile, they could fix fab issues with 7nm right now while using external foundries, and maybe get to being the head of innnovation
And then there is also the matter that even if Intel bought 100% of TSMC's wafers, it would still be nowhere near enough to meet Intel's requirements.