Not sure if the 10 overs would of helped as SL were able to bat the whole day and only lost 2 wickets. We don't know for sure as anything could of happened in them 10 overs but going by how SL were able to bat out a full day shows that it might of still ended in a draw or even a SL win. We got a fair idea that this would be a draw after the end of day 2, it seemed that both teams were playing for the draw at different stages of the match and even though the WI did declare as you said they batted for too long.
Well.. both the teams were targeting a draw, so it doesn't matter much. I though that West Indies had a chance if they made the declaration after scoring some quick runs. But the West Indian batsmen were too slow, and the declaration came with less than 10 overs remaining in the 4th day. And when Sri Lanka came to bat, there was no real effort from the West Indian bowlers to take quick wickets. Even part time bowlers such as Kyle Mayers and Jermaine Blackwood were called up to bowl.