On the 9% figure, it remains to be seen the extent to which the Olympics inflated turnover, so I take your point, but then of course how do you quantify how much CCFC contributed to turnover? There are monies that are directly attributable (that is payments made directly from CCFC to ACL), and there is indirect income that ACL earn off the back of the football club, which is more difficult to quantify - especially when you are talking about income from deals with Ricoh and Compass which were signed at a time when it was understood that the football club would be in permanent residence there.
Of course bottom line takes precedence over turnover (profit is sanity, turnover is vanity and all that), but for that type of business especially cashflow is vital. What having an anchor tenant provides is regular cashflow and stability. A situation whereby you have a series of one-off events spread out unevenly can pose problems. There is also some doubt as to the financial benefit of one-off events, and didn't the council actually have to pay for the staging of the Davis Cup (for which ticket sales were disappointing).
I think the Ricoh is probably viable as a venue without the football club, but would require a roof because open air events are so few and far between it would render the main arena pretty much redundant. I'm not a structural engineer, but can't imagine it would be that difficult or indeed costly (relative to the potential return) because you would ultimately end up with the biggest permanent indoor venue in the country and the range of events it could stage would be considerable.
But yes, I agree they must have made some contingency plans.