Electric cars can and did exist without computers. There was an electric car driving on the streets of Paris in 1859. [1]

I would argue it's the other way around: regenerative breaking is a nice to have, but good luck building a production ICE car without a ECU that comes anywhere close to meeting emission standards.

[1] https://en.wikipedia.org/wiki/Gustave_Trouvé#/media/File:Cap...