If Sri Lanka cannot give Bangladesh a lead of runs and if Bangladesh can start their second innings today, then it can be said that this Test between Bangladesh and Sri Lanka will be a 70% draw. But you can never say anything about the speed of Bangladesh's game with certainty. If Bangladesh falls into disaster, it can create an unwanted situation at any time. Sri Lanka need 128 more runs to equal the first innings score, but there is a high possibility that Sri Lanka will give Bangladesh a lead of runs and if they can give Bangladesh a lead of 200 runs in Sri Lanka's first innings, Bangladesh will be under pressure. However, there are two more days where a draw is possible and if Bangladesh's batting collapses, Bangladesh will lose.
You have hit on main points for this Test match. It looks like draw is very likely about 70% and I agree that especially if Sri Lanka does not get big lead and Bangladesh bats today. Big question is whether Sri Lanka can not only catch up but also get good lead maybe 200 runs or more which would really pressure Bangladesh. But Bangladesh batting can be unpredictable so even with two days left and draw looking probable sudden batting collapse could lead to unexpected loss. So Sri Lanka needs to bat well to set tough target and Bangladesh needs to avoid any batting failures to either draw or even win. We will have to see what happens with Sri Lanka next 128 runs and how they score afterward.