I can't predict how long your InfoPath forms will continue to work on SharePoint 365. Only Microsoft knows that. I don't have much knowledge about Microsoft Forms - last time I looked at them, they were pretty limited. If you start using FormsViewer with your list form, the form will still query from and submit to a SharePoint list. If your form is a library form, the XML will still be submitted to and opened from a form library.
Hilary Stoupa
