After Orkut was shut down, I think every other social networking site is doing its best to survive and reign in the market. Not only Facebook, even Yahoo Messenger is having video calling feature enabled. I think all the social media are participating in a running race, and each is trying to keep the other behind with yet another novel feature. I think Skype too would try to stay afloat in the current scenario, so they are too likely to come up with some more attractive features.
But each of these platforms has definitely got a speciality, which we all must have observed by now. Facebook is mainly for the purpose of finding new friends, while Skype is for connecting with the established contacts. So the focus of these two platforms make the users differ in their usage.
From the user's angle, I have seen that users can be broadly divided into two types. One are those who keep trying the latest feature that has got enabled somewhere and there is this other lot, who prefer to stick to the ones, which they became familiar with.
The people who got accustomed to Skype would most probably stick to their favourite site, even if others are providing better options as it is easy for them to do so. But yes, if Skype comes up with some new updates, they would happily accept them.
Personally speaking, I have observed in my friend circle, that each of them has developed a fondness for their own social media, and they are quite stubborn if you ask them about changing their habits.
Moreover, nowadays, as most of the children are staying away from their parents, the earlier generation got used to Skype and they have associated their interaction with their children through this app so much, that I doubt they would be that eager to change.
To sum up, I think each of these platforms are successful enough in building up their own target users. So even if a few users of Skype shift to Facebook, the rest would stay with them, so Facebook might not be able to completely wash off the existence of Skype in that sense.