Well, I applied for canadian visa two times (in 2003 & 2004) few years back. I had a six months visa each time. I did not have any problems as I took updated I-20, full-time status letter from DSO. You might be able to get your visa renewed in the canada, but why do you want to take your chances? I think the best option I see would get the passport from Nepalese embassy and go to nepal a semester before you graduate (do you have copies of old visa? may be your international office at school has it on records, take the copies with you just incase) and apply for visa. Make sure you have current I-20 signed by DSO before you plan a trip and if you can get a letter from them certifying the loss of passport and visa in regard to receipt from police, and all other supporting documentation you will be fine.