I believe the final series of Lost begins towards the end of January next year. I understand Flash forward consists of only 1 series and finishes next year to coincide with the date of everyones Flash forward.
I would think most producers would hope their series will last 5 - 7 years. If they have high hopes for their series the lead stars are often signed for those sort of durations. However, if viewing figures dip, then a series will be cancelled as it won't recoup it's production costs if no TV station wants to buy and show it.
Flash Forward ratings havn't been what they expected. It is currently on hiatus until March next year when there will be another 13 episodes.
I read an interview with the producer last week where he hinted there would be another flash forward black out and that they are hoping for a second season. The writer (Robert J. Sawyer) of the book Flash Forward that it is loosely based on will also be writing the episode set on Flash Forward day (April 29 2010).
It's entertaining but I'm finding the whole self-fulfillingness of it a bit annoying, e.g
'In my vision I get trampled by some elephants in a zoo - I have no idea how that situation could arise - I'd better get straight down to the zoo and investigate, so that I can avoid it happening'.
You feel like shouting at the telly, 'No you idiot, if you want to avoid it happening, staying the fk away from the zoo would seem like the best plan'.