John Gill Commentary 2 Kings 2:16

"And they said unto him, Behold now, there are with thy servants fifty strong men; let them go, we pray thee, and seek thy master, lest the Spirit of Jehovah hath taken him up, and cast him upon some mountain, or into some valley. And he said, Ye shall not send." — 2 Kings 2:16 (ASV)

And they said unto him, behold, now, there be with your
servants fifty strong men

Perhaps meaning themselves, (2 Kings 2:7) who were young, stout, and strong, and able to travel for days together.

let them go, we pray thee, and seek your master ;

For though they knew he was to be taken away, yet knew not for what time, and imagined he might be found again.

lest perhaps the Spirit of the Lord has taken him up ;

As it seems he was wont to do, see (1 Kings 18:12).

and cast him upon some mountain, or into some valley ;

Where he sometimes had his abode; or they might fancy, if he was taken up to heaven, yet in his soul only, and that, when that was separated, his dead body would be left on a mountain, or in a valley; and therefore they were desirous of seeking and finding it, that it might not be exposed to birds and beasts of prey, but that they might bury it in a decent and honourable manner.

and he said, you shall not send ;

He knew it was to no purpose, since he was translated to heaven, body and soul, and which he was an eyewitness of.