Guys, don't get me wrong, there are hundred of ways to ensure you have a "backup line", this doesn't mean we shouldn't have "revert back in case of failure logic"
How I ended up in this situation, I have changed "default domain" (entered two domains in the field) of the OpenVPN and I really haven't expected that, this is not supported and I also thought that, if it isn't supported the OpenVPN will simply return an warning, and ignore the value.
There is nothing related to pfSense in that case, it is up to the vendors of OpenVPN to clarify this as a critical or non-critical issue on the configuration and decide how to handle it - to continue, or to fail.
Anyway, I'm not here to blame pfSense developers, but opposite - to give them an idea to think of.
Meanwhile I remembered how the iXsystem guys do it - when you change network settings, you do your changes, then hit apply, because you are ready to test, then a simple timer is activated. If you don't save/confirm your changes in timely manner, they will be reverted back. (the same as Juniper, commit/confirm)