I agree with jags about rearward visibility, but one can always choose to use an LED blinky instead.
If I wished to terminate the taillight lead, I'd do so with a female connector (no exposed leads to short out) and then cap it with a (bolt) thread protector to prevent water entry. This way, you'd have essentially no lead left (except for a short stub, long enough to solder the connector, so perhaps 1.5cm minimum) while preserving the option to someday hook up a taillight if you wished.
I wouldn't just cut the wire and just leave the ends exposed. If you do cut it, best to cap it in some way. vinyl thread protector ca in black or some contrasting color will do the job. Heat-shrink tubing won't close the end as nicely.
Preferences can change over time, and if you plan to keep the light for a long while, this would keep options open. Alternatively, if you ever wished to sell it on, this would preserve the value over cutting the lead entirely.
As for warranty coverage, I don't think the result would be any different than simply trimming the end for a shorter run; the light itself remains unaffected.
Best,
Dan.