You are correct that lichen is harmless and not a factor in the tree's breakage. From the second photo, it looks like the branching was poor (a common condition on many trees, unfortunately) that made their points of connection to the trunk weaker and more likely to succumb to wind damage. The dark center on the fallen branch looks like wood decay that entered the heartwood through an old wound, possibly from the old branch stub we see in the center of the cluster of branches. By itself, this isn't necessarily a problem for tree health if it remains confined to heartwood (which is naturally dead tissue), but it does affect structural integrity of the wood. Included bark, which is bark that gets pushed into a crevice between branches rather than outwards (as it should be), is one typical reason branches with a narrow angle of attachment to the trunk can fail.

Unfortunately there's nothing you can do at this point because no pesticide is effective at halting existing wood decay, and it doesn't look like this break point occurred where it left a stub you can cut again to have a "clean" wound for the tree to seal-over. Don't coat the wound in anything, and you can always seek the assessment of a certified arborist about any other actions to take to prevent future limb loss (which may involve more drastic pruning).

The reduced flowering could have been from weather stress like low rainfall if it began last autumn, which is when the buds were forming for this year's flowers. (Or birds ate many of them...some songbirds do eat flower buds during winter.)

Miri