For the ice age I have this quote from Buterin on the next fork
"In general, if we get it out before the end of June it’s even better, and if we get it out before the end of August that’s still, like, less bad. My recommendation is probably still end of June as a … normal case target and end of August as a worst case deadline"
For difficulty it only took about 5 weeks to double and the price is starting to get stable around the high $300 close to $400 range
So a example estimate
Today 164 mh = $1000 month
~ July 24 = $500 month
~ September 1 = $250 month
~ October 7 = $125 month
This is assuming a static price with a static climb in difficulty, the climb will begin to slow as profit margins become thin for people and the gold rush ends. I think realistically you can expect profits to get pretty thin around November or December at best, unless price goes up. Vega will be a non issue, even if it did amazballs with hashing the limited units would be a drop in the bucket.