Well yes you can, but it is not recommended. If you are still on M1 after June 2020, it is akin to using a car knowing fully well that the engine and various parts which make that car function, will not have spare parts or suitable replacements. You are more susceptible to getting stranded and the car becomes very unreliable and costly to maintain.
Even the modules and extensions that you are using would become dated as the extension developers will focus more on investing on the M2 compatible versions of their extensions. Everyone will eventually move to M2, so they have no incentive to keep improving/supporting an older version of their extension.
So continuing to run your online business on a defunct system (after June 2020), is not a good idea.