As far as when Yahoo! will discontinue support...that's anyone's guess. They released 6.0 not SO long ago...so you may have some time...but just be prepared that you will have to back up your offlines somewhere else once you upgrade. Even the ones you already have saved and you think should stay there...they won't. I'm sure someone else will think of another way to get into the offlines...but the cellphone was the quickest way I could think of that worked for me.
We'll figure it out one way or another...you've come to the right place.