DWI in US never goes away...its stamped on his forehead forever if he wants to live in US. it goes away only from driving record after 5 yrs, but never from your criminal record.  Good thing is, this is his first arrest, It is not going to effect on you status or anything. it has no effect on H1-B, Greencard, Citizenship later when you apply for them (if that was his only DWI), and if he gets second DWI arrest...its better him to forget about US. he will get jail time also in that case for sure...now, you can go back nepal, and re-enter as usual. sometimes the embassy back in kathmandu takes a month or somthing to get information from US, FBI about the crime report on your fingerprint before they issue the visa. but in couple of my friends' case, they didn't have any problem.

now, he missed the court date, its a big big issue....I have no idea about it. all i know is, they send you notice couple times i guess, and they issue arrest warrent. its bad specially if you miss court date, or didn't provide a specific reson for doing so. the hope is, if he was deported by DHS, then he can explain to the court what happened, and probably wil be fine.