Maybe they won't make it back. Lots of people sailboat across and don't make it
She has such a high profile that I doubt any country's coast guard would want to take the blame for "why it took them so long to respond to a may-day."
I don't have any basis to say that there would be assets effectively "shadowing" her but I wouldn't be surprised either.
Greta's fan and support network may have contingencies in place too.