So it there's no immediate financial purpose to selling the new fund, just let it ride in perpetuity?
Can't write about VFWAX (never owned it).
VTSAX and VFIAX have basically the same returns
over the long run. In the short-term, one fund may outperform the other. But years later, they have performed similarly. That's not guaranteed to repeat in the future: e.g. if US corporate/tax law changes to benefit the megacaps or small/mid-caps companies to the detriment of the other, for example.
Also, VFIAX has 30 day S.E.C. yield 1.97% (100% qualified dividends). VTSAX's S.E.C. yeild is 1.87%, and it self-reported that the fund distributed 5% nonqualified dividends in 2018. Some minor financial differences.