You have the potential to get the money back into a traditional IRA and subsequently convert it to Roth in 2019 or later if the financial institution will accept the late rollover back into the traditional IRA of the money withheld for taxes as I described in my previous comment. If you have documentation to support your assertion that you requested that nothing be withheld for taxes, it seems reasonable that this could be considered financial-institution error. With such documentation, it the financial institution should be willing to accept that they made a mistake and accept the rollover. Such a late rollover will be reported with code SC in box 13c of the 2019 Form 5498 from the traditional IRA. The portion rolled over late would be reported on your 2018 tax return as an amount rolled over.
