Yes, according to the book Night Elves have send all their army to the Silithus. They were planning to stop entire Horde, alone, with their army. So army was pretty big.
While only city guards and rookies were left, to defend the lands.
That’s why Horde army was 8 times bigger in the War of the Thorns. That is why Night Elves, race that is so popular with their druids, had only about ~10 druids at that battle, and no Hippogriffs riders e.t.c
At the end of the war, fleet have returned. Ships started to shoot from cannons. But soldiers were staying on the ships. There is also mentioned, that Night Elves were waiting until other ships, the bigger and slower ones will return.
Offtop - in WoW there are no Night Elves War ship model like in Warcraft 3. Only transport ship.
Later, Horde managed to capture one ship. Another 2 ships were burned down by orcs shamans. Then, Shandris ordered to flee back to the sea. She was planning to attack on Teldrassil, when it will be captured by the Horde.
In other words according to the books, fleet with main army survived.
Later, in game, after Teldrassil was burned down, there was some changes during 2 next weeks on Darkshores. About 6 Night Elves ships were in battle with Blood Elves. Another ~6 ships were just standing in the sea. Another 2 ships with refugees and a small army appeared on the North.
Also Dryands appeared there building some barricades. And moon priestess were creating some moon stones there.
I have no Idea why those Night Elves were shown. But later they were just removed.
In table missions is mentioned, that Night Elves are continue to evacuate refugees from Teldrassil, by the sea. That is happening after the Burning of Teldrassil.
Probably those were refugees from Rut’theran Village. Those who were close to water and could survive.
Also in Stormwind one Night Elves ship stands broken. With words that this ship brings refugees.
A couple of more Night Elves ships were shown different locations of BfA. Even at ZulDazar were Alliance fleet was destroyed, there is one destroyed Night Elves ship.
What my point is, that yes, the feet with soldiers survived. This is where Tyrande found soldiers to created Army of the Black Moon. This is where Night Elves found soldiers for suicide mission. This is where Night Elves managed to find soldiers for different war missions, invasions, and quest in BfA.
Also this is from where Nigh Elves found soldiers for last siege of Orgrimmar.
It was not a cloning machine. It was army of the Night Elves.