Diablo Free?

Well, I decided to take a week off work next month for the release of Diablo III. I'm not sure I'll spend the whole time playing D3 in particular but it's high time I've had a vacation anyway and it's not like I'm particularly prone to doing anything else with my vacation days from work.

Blizzard announced a while ago that you could get a copy of D3 free if you took a 1 year contract for World of Warcraft. It turns out that offer expires very shortly (next Monday). The question is... Would it be worth signing back up for a year? Just how much of a savings would I get, and could I possibly play enough World of Warcraft to have such an option make sense? I decided to take a look to see what information I could gather to help make that decision...

• Diablo III is going to cost $59.99 if I buy the digital version. Same price at EB.
• Collector's edition is $99.99. It combos with the 1 year thing by giving you an extra 4 months of WoW free.
• The collector's edition looks like it has nothing at all that I want. So I'm going to ignore that option.
• One year of WoW at the cheapest price is $155.88.
• I am unlikely to sign up for 6 months at a time if I start playing again on my own outside of this contract. Probably more like $13.99 per month.
• No one really knows when the next WoW expansion will hit shelves. Maybe around September. The beta is already up so it seems pretty inconceivable that it won't hit during the year contract.
• Run all that math together and I'd need to want to play for a little less than 7 months to 'make money'.

So the question is, would I play for 7 months? I wouldn't mind going back to the ironman challenge even before the expansion hits. Likely if I was playing after the expansion hits I would play for 7 months to make it worthwhile... If it launched by the end of September, anyway! And even that is barely break-even... Worse considering I have to pay upfront and don't get to choose not to play WoW in 7 months if it turns out I don't want to. The upside is I would get the possibility of playing over the next 5 months before the expansion hits when I feel like it. Without feeling the obligation to play a lot because of paying a monthly fee... 

I'm conflicted. At least I have a week to decide!