If he has been classified as deserter, he could well be arrested upon arrival.
Read Melvyn Tan's case for reference.
http://en.wikipedia.org/wiki/Melvyn_Tan
However, your friend may well receive a harsher sentence if he's a mere peasant. Melvyn did a plea bargain ahead of time and he's also a celebrity of sorts.
Boss, Melvyn's case is slightly unique.
Firstly, Melvyn has zero intention of coming back as he know that once he step his foot in Singapore, he will be caught as a defaulter. He was invited to Singapore on a red carpet for some musical event. If my memory serves me correctly - to be a judge in some premier musical event.
Next, this invitation is by the Tourist Promotion Board (again based on my memory). Tourist Promotion Board is under a stat board under a ministry. :*:
That makes his case unique.
He got away with it by paying a $5000 fine in addition to the forfeiture of the $75,000 bond paid by his parents.
Now with that $80,000 paid up, cheaper than a Cat B COE, he is now free to travel in and out of Singapore.
Because of his case, that ridiculous TCH and NEH made it a rule that all male Singaporeans who are studing overseas MUST return to serve NS once they turned 18. Yes, they could be in the midst of their uni program. They will have to apply for deferrment from whichever uni they enrolled, to be back to serve their NS. No exception allowed. Except of course those scholars and you know who...