If I get rejected from being a finalist and decide to apply regular decision through questbridge, can I still apply to those schools or any schools in general via common app?
The schools will keep your QB app on file and reconsider you in the RD round. No need to reapply using common app
I’m pretty sure if you do not become a finalist, they don’t forward your app for regular decision. They only do this if you are a finalist and don’t match with any of the schools. If you are not a finalist you have to apply to college regularly through the common app
https://www.questbridge.org/high-school-students/national-college-match/non-finalists
If you are not selected as a finalist you can still apply at many of the schools with the questbridge application (usually supplements are required though.) You can also apply normally through the common app.