It is not right to be sure that Bangladesh will win without seeing the end of Bangladesh's innings. Bangladesh is a team where if there is a batting disaster for some reason, it doesn't take long for wickets to fall. However, Mehdi Hasan Miraj and Tawheed Hriday remain unbeaten on wickets, so for now Bangladesh has a chance of winning. If Bangladesh can bat full fifty overs in a defensive manner then definitely Bangladesh will win. Moreover, Mushfiqur Rahim and Mahmudullah Riyad still have two finishers, so it can be said with confidence that Bangladesh will play well and win for the time being.
You are absolutely right in your concern that we should not assume that Bangladesh have won the match until they actually win it. They need another 100 runs in 17 overs but the problem is that they are losing wickets and now only 3 wickets are left with them. All the set batsmen Soumya Sarkar, Najmul Hossain Shanto and Mehidy Hasan Miraz have lost their wickets and now this task is becoming difficult for them. I think they may lose this match.
Here i would like to mention some super bowling spells by AM Ghazanfar. He took 5 wickets in his 6 overs that he bowled. The famous Rashid Khan also took 2 wickets and the Afghanistan team who were looking that they may lose, are now on the verge of pulling it back and snatching the win from the Bangladesh team.
Ghazanfar who had 4 wickets from his 5 games today done amazing job for Afghanistan as off spinner took 6 wickets which is surely career best figures for him and huge win for his team as well.
Worst performance for Bangladesh as they go down from 120 to 3 to 143 to 10 what a change in this game we have completely dominance of bowlers first two seamers done good job for the Bangladesh but at the end we have all rule of spinners as we have 9 wickets for spinners which give another win at the Sharjah to Afghanistan and humiliating defeat to Bangladesh.
After Shakib ul Hassan this team is totally crap as no one having ability to lead from front and give good support for having win things are completely down for them because this is big below as they were in control after end of first inning.