Umm... I've had perfect fruit on my trees for longer than 30 days and they are 100% fine. Perfect fruit's rotten-ness is based off how many times you shake the tree. Each time you get fruit from it successfully and the tree doesn't die, it has a higher chance next time.
Anyway, I don't really understand why you can't bring your 3DS with you? I get that there is no electricity, but the 3DS can still last quite a while--especially on power saver and with low light and the wireless switch off. I'd play a little each day and then turn it off. Just to check on my villagers and flowers.
If there's no villagers you care for, just leaving the town on a Beautiful ordinance should be fine... however, your hair will become messy after 14 days so if you do take it, I'd recommend checking it like every 10 days.
If you have villagers you care for, the best thing I would say to do is actually play ahead the month and then, on the day you'd be returning home, constantly reset that day to 6:01AM each day (so the day never changes) and just do that for the month. That shouldn't kill the battery and keep all your villagers fine.
Edit: Also, if you really don't want to take it, you could always turn your 3DS' time back to the day you left and play the month you were gone to get back to where you were (just, obviously change the date through the 3DS). This should leave everything in tact.