Many of us have tried to come back after even just a few days of not playing, to see everything has stopped on the island.
My suggestion is to be able to give someone "babysitting" privileges from inside the game.
Let's say player 1 needs to go on holiday for 2 weeks. He can then appoint someone to be a babysitter (player 2), and from a control panel give permissions as to what player 2 can do on the island. He could be allowed to build buildings, send explorers, trade and so on. Player 1 just need to allow which things player 2 can do on his/hers behalf.
Player 2 can get a possibility to "visit" player 1 like always, but now player 2 can do more than buff buildings.
This way it doesn't need to take the most of a day to rebuild the entire island back to working again.
To prevent abuse, the babysitting could be for a limited time as well, say 3 weeks and then player 2 cannot babysit player 1's island for the next six months or one year.
I'm pretty sure someone already helps out each other, but it has to be with the users name and password.