dumb question: If a pre-sequence star is assimilated into a larger EOL star, does all the newly assimilated fuel delay or accellerate the larger star's demise?
It may prolong life by a few million years. A red supergiant's outer layers still have a few solar masses worth of hydrogen, and the extra material would delay the collapse of the star onto its core.
On the other hand, if the merger happens after the star has started burning carbon, it would have no effect. The explosions and collapses occurring in a supergiant are driven by successive phases of nuclear fusion in the core (collapse when one kind of fuel is exhausted, explosion as the previous fusion products become fusion ingredients), and they happen on a very short timescale (starting at thousands of years and ending at days before the star goes supernova). The presence of lighter elements billions of km away would not really have any impact on that.
