This is a very prescient thought; Toyota has, in the past, entered a class with an engine, pushed it hard with considerable funding, became the must have engine, and when participation in the class no longer was of value to their marketing, departed. That pull-out left owners of the engines without a parts source. The class almost collapsed, but has survived with an assortment of other engines. The class in question is the SCCA's Formula Atlantic. In its Pro years it was a stepping stone to Indy cars, and later as a club class produced large fields with very good racing.
It may be that as long as Toyota remains in NASCAR, the Midget engine program, as an offshoot of their NASCAR effort, will remain supported. When road cars have moved far enough towards electrification that combustion engines are on the decline, participation in NASCAR will no longer be of value to Toyota. At that point Toyota will leave, and the Midget program will also be over.