Were people saved from their sins and gained salvation before Jesus came on the scene? If so, then Jesus was unnecessary. If not then they must have died without being saved. Then, assuming Jesus was needed, salvation was only to be had through belief in him.
Acts 4:10-12
be it known to you all, and to all the people of Israel, that in the name of Jesus Christ of Nazareth, whom you crucified, whom God raised from the dead, in him does this man stand here before you whole. 11 He is ‘the stone which was regarded as worthless by you, the builders, which has become the head of the corner.’[a] 12 There is salvation in none other, for neither is there any other name under heaven, that is given among men, by which we must be saved!”
As explained in Gill's Exposition of the Entire Bible this passage means:
"Neither is there salvation in any other,.... Meaning not corporeal healing, but spiritual and eternal salvation; the Syriac version renders it, neither is there "redemption in any other": Christ is the only Saviour and Redeemer,"
Logically then, those, who for whatever reason, didn't get the message lost out on salvation.