They are required to send it to the IRS, but that's not to say that they will since they are likely to be subject to a penalty for filing the form late. They might just hope that no one at the IRS notices. If the IRS does notice, you'll be the one left holding the bag unless you can document with your copy of the 2016 Form 5498-SA that the contribution was made for 2016. Be sure to keep the one they send you forever in case the IRS ever does think that the contribution for 2016 was an excess contribution for 2017 that would be subject to annual penalties.
