They have 200 solid episodes written already. And by the end of it, if its rocking the TRPs they will chose one way to move ahead with the storyline and do it. And if its not doing well (i doubt) they will have a different ending planned.
Either way 200 episodes/1yr is already in contract neither party can breach it.
Anyway its too early to think about stretching! If a well planned and executed script that doesn't change due to TRPs(cz hopefully it will be so awesome that it will be accepted as it it) then they can have a solid storyline for around 3+ years too.
As this is not a rushed show, they have a solid storyline for a long period of time in place. And quite lot of it broken in to episodes and written down too..
As its kind of like a first for Indian TV to have a bound script like this, let's watch and see. As its a lot of firsts to the channel, PH, actors and us viewers all alike..
I just wish a wonderful run with very high TRPs for this show! Hopefully with a solid story for a good 3-4 yrs!! *fingers crossed*