After the subscription expires the plugin will continue to work just as normal. You just won't get further access to updates of the pro version, or premium support via the ticket system and will not be able to access the Optimize Images API.
Refunds are only issued if you report an issue that we cannot resolve for you in a timely manner. This doesn't cover if you cannot use the setting you want to use as not every setting works on every website. Read our Refund Policy here.
You can use the plugin on all your sites and domains. However, if you are a developer that optimize sites for clients, then you should subscribe to the Developer package. You also get to create unlimited download ids for your clients with this package.
With your subscription you get access to premium support via the ticket system. If you have any trouble configuring the plugin or resolving conflicts, we'll do it for you if you can provide administrative access to your site.