Originally Posted by jsloan

There are too many variables here to give a clear answer. If you try to get an FFC, your fare will be recomputed on a one-way basis. On international itineraries, it's common for a one-way flight to be much more expensive than half of a round-trip. (In fact, sometimes it's more than the entire round-trip). EWR-BOM and BOM-EWR appear to be a mostly symmetrical market -- which doesn't always happen -- where one-way tickets start at about $850. So, (a) that's the amount that you should expect UA to keep from your original fare if you try to get an FFC. But, (b) that's also the amount you should expect to pay for a new one-way ticket in order to use the return trip if you defer it. Then again, (c) it's not necessarily as simple as "just find T availability" -- all of the conditions of the original fare need to be met, including maximum stay requirements. So, if your original fare has a three-month maximum stay, and you try to push the return out beyond that, the entire trip needs to be re-fared. (You can check your fare rules via a link on your itinerary screen).

My default approach for this situation would be:

(a) unless you have an overlapping flight that may draw UA's attention, don't make any changes until your return trip is about to commence.
(b) if there is a significant schedule change or a cancellation, ask for a refund of the un-flown segment. In this case, they will not re-fare the original ticket; they'll refund it on a half-round-trip basis. (You may not get exactly half the original purchase price back; for example, if your outbound was a higher fare class than your return, you'll get less than half. But it's almost always better than re-faring).
(c) if not, you can cancel at that point and proceed with whatever you decide about getting FFC or changing to a new date. Note that changing to a new date doe not preclude you from getting an FFC at some future date if it turns out that you don't need to travel after all.