You would need to review your 401(k) plan agreement or ask the plan administrator to be sure, but given the 60-day grace period, it seems likely that this distribution will have occurred in 2016 and will be reportable on your 2016 tax return. I know of no situation where a retroactive distribution can be made from a 401(k).
Presumably you would simply pay back the loan if you had the funds to do so and you 401(k) balance was high enough that you are permitted to maintain the 401(k) account with this employer, but since you are no longer employed with the company, the plan should be processing this distribution as an offset distribution which is eligible for rollover rather than a deemed distribution which is not eligible for rollover. Since you've already received the money (the loan outstanding balance) for which the offset distribution is being made, you would have 60 days to come up with the money and complete the rollover to another retirement account.
