aka "Herr Doktor Hubert"
Yup - see p. 71 of the Sword Coast Adventurer's Guide. Or at least, it "was transferred to another world, much like Halruua". Abeir sounds like a likely candidate, and it wouldn't be surprising if families of gnomes with strong mechanical aptitudes showed up in Maztica during its time on Abeir - especially if they thought the... political climate back home became uncomfortable. Heck, they might even have brought the printing press with them. Of course, Maztican hieroglyphs are not ideally suited for printing, but perhaps they developed a transliteration based on Draconic letters (which is likely a major trade language in Abeir).
Anyway, let's discuss religion. While the gods rule Toril, the Primordials/Dawn Titans rule Abeir. So, from the perspective of the inhabitants of Maztica, divine spells and prayers to their gods suddenly stopped working when the Spellplague hit. I would only make an exception for the goddess Maztica, who is in some ways the land itself and whose priests are essentially druids.
It's likely that some cults start sacrificing hearts to their gods in large numbers in the hopes of bringing their patron deity back. These cults are eventually driven underground by the dragonborn - not out of humanitarian concerns, but because human sacrifices are a waste of perfectly good slaves. Most faiths decline - what use have the Mazticans for gods who have abandoned them to the mercies of first the Amnish, and then the dragons? Only the cult of Maztica gains new followers, and may change from a purely wilderness cult to one that spreads to the cities.
Then, after the Sundering, the gods start answering prayers again. However, the Mazticans are wary - if the gods have done nothing for them for more than a century, then why should they now receive worship? While the cults do revive and gain new followers, these cults are nowhere near as dominant as during the pre-Contact era. The God Helm, of course, is even more contemptible - the so-called "Guardian God" did nothing to protect the Mazticans from the Amnish, and then he abandoned his own followers in turn when the dragons came.
So right now, Maztica represents a "market niche" for proselytizing faiths, and missionaries of all kinds will quickly flock there. Of course, the Mazticans will be less interested in tales of how awesome a specific god is and more what the god can do for them and their families... which will usually mean "what the priest can do for them". Still, there is plenty of opportunity for ambitious priests. Wakueen will quickly gain followers among the merchants, for example... while Bane will try to appeal to the more draconic instincts of the dragonborn. The Platinum Cadre will also try to gain converts, although worshiping a dragon deity (Bahamut, in this case) will likely be as unpopular as it was in now-vanished Tymanter.
From a meta perspective, this also provides many reasons for intensive contact between Maztica and Faerun. After all, there is little point in developing Maztica as a region of the Forgotten Realms if it is completely isolated from the more familiar parts of the setting.