The way United, Spurs, and Liverpool are playing this season, as little as 65 points may be enough to clinch 4th place.
Leicester already have 43 points from 21 games, an average of 2.05 pts/game this season - good enough for 78 points when extrapolated over 38 games.
As such, to reach 65 points from now they only need another 22 points in their last 17 games, or an average of 1.29 points/game. The 65 point mark could feasibly be even lower too, meaning that just better than relegation form (19-20pts from 17 games) could be enough for Leicester to get 4th.
Of course, this assumes that not more than one of Spurs, United, and Liverpool (or West Ham, Stoke, and Palace) shoot up the league to raise the threshold between 4th and 5th higher.
With all this in mind, I'd say that it would be more surprising if Leicester weren't in the top 4 at the end of the season than if they were.