Can additional market press payment gateways live outside the market press plugin folder?

I wrote a few custom payment gateways and am writing more.

1. However, I am concerned that if market press updates, i might lose my payment gateways. will this happen?

2. If dumping my custom payment gateways in the plugins-gateway folder will remove my gateways after an update, then can my own custom gateways live outside the market press folder? that means it will be its own plugin. Can I just dump my existing payment gateway file (which i copied as-is from eways/paypal/manual payments), into the wordpress plugin folder or do i need to write additional code? can u help me with the code for this?

3. one of my gateways that i'm writing has an interesting reseller option. i will need to add this option in the network page. however, i shouldn't make these changes in marketpress-ms.php as i think i might lose my changes if market press updates. i believe i need to write a new plugin, but how do i override the marketpress-ms.php html and php code so that i can add my code?