"does client have to convert to ROTH /other retirement plan or distribution?"

No. The provision to convert is available as an option; not as a Has To. When they convert and however much they convert, this $5,500 is part of their basis and any conversion will take into consideration basis + earnings to get the % taxable, across all Traditional IRA account balances at the time of the conversion or distribution (which won't be 2018, obviously). It isn't clear why you asked this part.