Subscription based software is incredibly unappealing. I don't buy in. I have no desire to pay monthly or yearly for things I may or may not use. I want to buy the tool and that is the end of the payment scheming.
Anything that requires constant internet connection is also a no-go - won't buy. Internet connections are not reliable.
I haven't seen anything in the terms of an Office 365 subscription that says you can't cancel it. In a lot of ways, the subscription model is very appealing for software you're either not sure you're going to use or you're going to use a lot.
If you're not sure you're going to use it, just pay for a month and then cancel it. You're only out $10.00 as opposed to $200 or more if you went and bought Office off the shelf. If you decide you need to use the software again, activate your monthly subscription again when the time comes.
If you're going to be a regular user of the software, you keep paying as you're using and in return, you'll get always up-to-date software.
To your statement about internet connections being unreliable, I have to ask, where are you located in the world?
Here in the U.S., I can use my iPad or iPhone going down the highway at 70 MPH and still get 15-20 Mbps down over Verizon LTE. If you don't go for the absolute cheapest internet provider you can get, you should have a reliable connection. If you don't have a reliable connection, it's time to consider switching providers. We live in 2013, not 1997. . .reliable internet connections aren't difficult to find in many parts of the world these days.
Also, I don't think the Office 365 subscription requires that the internet connection be up every time you want to run the software. If it's like the other software subscription services, the software is physically on your device or machine and it only periodically "phones home" to make sure the device or machine is linked to an account that has an active subscription.