Even though the short term risk is small the potential damages are enough to justify funding a few geologists to properly study this. If the risk seems real they should run computer models on just how big a splash this volcano would produce, then repeat the computer run with all the above sea level material digitally removed. That should shrink the tsunami somewhat and might reduce it a lot. If the risk seems imminent, say in the next 50 years, then why don't we just strip mine the offending mountain part down to sea level. It would take some time and money, but the technology to do it exists and if these catastrophic projections are correct than it should be much cheaper than a natural splash. However if the purely underwater portion of the collapse is enough to cause a catastrophe then our choices are more limited. I doubt current underwater mining technology is adequate to remove the problem. At best we could prophylactically throw W into the volcano as the MSM will blame him anyway for the massive loss of blue voters that follows.
A lot have carefully studied Cumbre Vieja and many people have roundly debunked the scare stories which fostered a bunch of sensationalistic documentaries - however,
1) while scientific journals have reported on this, the MSM has not
2) a lot of people on the internet got off so much about fantasizing about Cumbre Vieja wiping out the East Coast they don't bother to look at any of the counter-evidence.
http://www.sthjournal.org/media.htm
http://www.lapalma-tsunami.com/
The collapse of Cumbre Vieja and the subsequent tsunami has a far higher propability of coming true than Global Warming does. We would be far better off directing the billions currently being spent to reduce CO2 emissions to doing as you propose, strip mining the sides of that mountain and using the rock to expand the island. The locals would benefit, and think of the all the condos that could be built on the new land.