Removed payment method, old orders not loading

Yes, it is possible to strip down the extension to just provide the payment method. I recently did the same for the replaced extension Saferpay_Business. just removing the extension will prevent the users from viewing their order history and throw an exception in the shop backend whenever one opens an old order.

just disabling the module output unfortunately is not enough: observers will still be called which might lead to nasty side effects. in our case, the saferpay extension added extra js files and changed headers through an observer, which prevented the onepage checkout to work properly.

here's what we did to strip down the extension:

1. removed <resources>, <events> and <routers> entries from Saferpay_Business/etc/config.xml

2. set <show_in_default>, <show_in_website>, <show_in_store> to 0 in Saferpay_Business/etc/system.xml (will hide the specific payment settings in the admin)

3. removed layout changes/override entries in <layout> from app/design/base/default/layout/saferpaybe.xml

4. change the version information in Saferpay_Business/etc/config.xml to prevent updating the extension if it's still available in magento connect.

your steps might differ - try in a testing environment first.