Did Gollum deserve death?

[Kuruharan]

it was quoted earlier that even orcs were given mercy if they asked.

-and-

And those that were deepest and longest in evil servitude, hating the West, and yet were men proud and bold, in their turn now gathered themselves for a last stand of desperate battle. But the most part fled eastward as they could; and some cast their weapons down and sued for mercy.

That passage does not refer to orcs.

Note:

And those that were deepest and longest in evil servitude, hating the West, and yet were men proud and bold

The orcs were...

orc or troll or beast spell-enslaved, ran hither and thither mindless; and some slew themselves, or cast themselves in pits, or fled wailing back to hide in holes and dark lightless places far from hope.

It didn't occur to them to beg for mercy. They weren't rational anymore.