Insured Welfare Plan - Final Return

Say a fully insured group health plan covers 100+ participants. The company (plan sponsor) is sold during 2017 and the group health plan ends, and the policy expires, on December 31, 2017. The employees are hired by the acquirer effective January 1, 2018.  

The 5500 instructions say not to check "final return" if "the plan is still liable to pay benefits for claims that were incurred prior to the termination date, but not yet paid." 

Two questions:

1. Is 2017 the final return, or does the fact that the insurance company may still receive and pay claims require another 5500 for 2018?

2. If the answer above is yes, presumably the active participants at the end of the plan year would be 0, even though the policy ended at 11:59 p.m. on December 31, 2017, correct? You can't file a final return with a participant count >0, so this seems logical. 

2017 is the final return.  Active participants on 12/31/17 is zero.

Thank you!