(Sorry, this is a really long post...)

Yeah, I think a reminder would be nice but not too many or too soon (I can sometimes be inactive for a couple weeks if school gets busy and I would be really annoyed if I got twenty emails about it).

So first off, it needs to only be sent after a considerable amount of time has passed (1/2 year or an year? Maybe 2?)
Secondly, I think the email should clearly list the player's options: a link to Sylestia where they can log in / reset their password or whatever so that they can continue playing, an option to be reminded again in x amount of time, or an option to delete their account.

The first option is pretty straightforward. For the second, I think it would be useful for people who know that they're too busy right now but would like to play later on and don't want to forget about it. Maybe they can opt for weekly or monthly email reminders or a single email in this many months.

Now for the third option, I'm rather conflicted and I know many others are too, so I will briefly outline my thoughts. Please note that I'm suggesting a voluntary deletion, not automatic.

On one hand, Sylestia is growing quite rapidly and having an increasing number of pets from inactive players would probably not be great. Deleting an account that you know you will never have time to get back to will help reduce the server load (I think, I really don't know how much work it takes to run this site).
On the other hand, many old players have rare and valuable pets that would be a shame to lose. A possible idea would be to open a pound where players can adopt these pets (like chickensmoothie's pound). If I were to ever leave Sylestia, it will probably because life got too busy. This means that I would likely not have time to have a giveaway even though I would really prefer for my pets to go to other players instead of being released. Now I know that overpopulation is becoming a real problem so I would suggest that pets in the pound would only be available for say, a month after which they would be released. This allows players to save the rare pets but avoid overpopulating the site. And maybe current players can contribute pets to the pound as well...

Again, sorry for the long post. I didn't realize I had so much to say about this topic >.<

No, it's fine, that's what I've been trying to say (you just explained it better haha)