Template:M summ 1992 ISDA 6(b)(iii)
Handwaving appeals to one another’s good natures with this talk of reasonableness and, of course, both parties will probably be incentivised to keep the trade on foot if some unfortunate tax eventuality comes about — seeing as they were incentivised enough to start it —but ultimately, this is an agreement to agree, however you dress it up, and is as contractually enforceable as one. That is, not very.