C.S. Lewis has a nice expression with this regard: "I believe that nobody comes to Father but through Christ, but I do not know if only Christians come to Father through Christ".
In fact, what is it to be "saved"? It is to be fit to the Kingdom of Father and Jesus, which is one Kingdom; but who is fit to the Kingdom? Only those who live according to Christ's commandments, for, if you are a tough guy from a street subculture and avenge when wronged according to the terms of this subculture, how can you be a citizen of Heavenly Jerusalem, i.e. of Jesus' and Father's, and Holy Ghost's kingdom, in which only those live, who forgive each other? But who can forgive? Can man forgive by his own efforts alone? Were Romans stupid to coin a proverb "to err is human, to forgive - divine"? The Gospels teach similarly, that we cannot do those divine acts without Christ acting in us (John 15:5), which action is called "working of His Grace in us" and we co-acting with Him. Thus, it is our joint merit when we forgive, for divine grace cannot work automatically in us, unless we co-act with this grace, at least to a certain extent. Just think about a poet getting inspiration and writing a wonderful poem: is it only his Inspirer-Muse to be given merit, or also this poet who entertained this Muse and took pen and in pangs of creativity presented to the world the poem? The same in co-action of man with divine grace working in him. Thus, it is impossible to enter the Heavenly Kingdom without Jesus Christ acting in us and transforming us into new creations (1 Cor. 5:17), fit to the Kingdom.
Thus, no salvation whatsoever without Jesus Christ, be it known to all wrong-headed liberals who say heedlessly that "all religions are the same" and similar crap.
However, when Jesus establishes His disciples to preach His commandments to all nations, does He Himself care not for those pagans who were not reached by His apostles and could not be reached physically, simply because of distances and the level of communications and transportation? Just think: Paul preached in Thesaloniki, but could not go to, say, Larissa; were Thesalonikian pagans any better than Larissians? Or does Jesus love more Thesalonikians than Larissians? A stupid calumny on Jesus if we say this, for He created the entire humanity with the Father, and how can He not care for all? So, can we deny that He cares also for those people who were not reached by the Apostles? No, we can not, unless we cease to be not only Christians but even plain homo sapienses with healthy brains. And if He cares, He cares to what aim? To the aim of their salvation or something less? Of course to their salvation, for how can we belittle the extent of Jesus' care for mankind?! I leave open then the question how does Jesus care for all humans regardless their anything - religion, customs, agnosticism, atheism etc. - and in what mysterious ways does He treat them or judge them or forgive them. This, of course, does not mean that preaching is unnecessary since Jesus cares anyhow! No, and thousand times No! This will amount to a same stupidity as when a doctor who can help an ill person by his medical skills and medications would say: "Why should I use my medical skills, does not God care for him?" - Yes, God cares for him, but now He cares through your medical skills, as now God cares for pagans through your, apostles' preaching! But, if there is no doctor, will anybody hinder God to help the ill guy by His invisible agency? Before vaccines, could not God hear prayers of people in pandemic and stop it at will? This does not mean that I suggest prayers instead of vaccines, when the latter is available through science, for this will be already testing of God, which is sin.
I think, the working of Jesus in pagan cultures can well be evidenced in pagan literature and philosophy, in great wisdom of Greek writers and philosophers, - just read Plato, how could he have guessed all those great and wise things without divine help? Or read Lao Tzu, how could he come to those wonderful ideas without inspiration? I do not say that one can be saved by reading Plato or Lao Tzu, again No! For Plato and Lau Tzu themselves cannot be saved without Jesus. In fact, after the Incarnation Jesus taught all humanity already to a different and far surpassing level than any of the pagan greats, but the latter's great and truthful ideas were also from Jesus. When Homer celebrates in the last song of Iliad the forgiveness between arch-enemies, and what arch-enemies - of Achilles, a killer of the beloved son of Priam, with the very Priam who found in himself a divine power to forgive Achilles; yes, when Homer celebrates this, can he do it without Christ inspiring him? St Basil the Great did not think so, saying that Homer is a divinely inspired author and urging Christian youth to read him.