suddenly dead trees, some splitting open
We have had a number of well established trees die this past year. After several years of drought we had an exceptionally wet winter. No hard freezing here. We have lost redwoods, poplar/cottonwoods, Italian cypress, willow, fig (black) and fig (white).All died seemingly spontaneously. The fig trees, now dead, are splitting open on the trunks and limbs.
These trees are dead - past "tracing".
The cracks were not caused by freezing- as in "frost cracks" and it is the trunks, so not "bark splitting" either.
This is likely caused by the fluctuation in the environmental conditions you mention.
Wounds should not be covered; there is a technique called tracing, that is explained in the links below.
You can also check with your County Extension Office, they may have specific care to your region.