The problem is that the Church recognizes all marriages which conform to the civil law as valid marriages, provided of course that the two people are free to marry. She does not automatically disqualify Jєωιѕн, prot, civil etc. marriages as invalid - so Catholics who get married by the Justice of the Peace, actually are considered sinful but valid. It would seem in their quest to save insurance / money, they did so at the expense of committing sin.
Would they get divorced if their plans involving the civil ceremony didn't work out as planned or would they simply forget the whole thing as if it never happened?
They're not valid marriages if they're baptized Catholic(s) and get "married" outside the Church. Canon law is pretty clear about that. I didn't go to my brother's wedding because he married a non-Catholic outside the Church (albeit he hasn't been to mass in 10 years).
Well, from the OP, looks like the marriage was valid, sinful but valid. What about if their plans didn't work out - would they simply forget the whole thing as if it never happened and go their own separate ways? get divorced? get an annulment?
There are Church Laws regarding marriage. They are all framed with the recognition of the holiness of the sacrament and the gravity of it - and the need that we have for not only the grace of the sacrament, but also for the directives that the laws contain.
I assure you that CL does not permit Catholics to get a civil marriage for convenience sake, then finalize the whole thing all over again with all the trappings officially within the Church when it is once again convenient to do so.
Let me put it this way - if it were me and I were to do that for any reason, I would be validly married and would be committing mortal sin by getting married outside the Church, that's the way that works for me. If your relative found a loop hole, please spill the beans as I am sure there's a few couples out there might like to partake.