Is there any tradition of Israelites leaving Mitzrayim before the Exodus? Moses fled Egypt on his own. Was this a unique occurrence, or is it safe to assume this was a regular thing? If it ever occurred, what happened to these Israelites?
"The tribe of Ephraim miscalculated the time of the deliverance of the children of Israel from Egypt, and left the country thirty years before the appointed time. They were met by a hostile host of Philistines, who offered them battle, in which the Ephraimites lost 300,000 men (according to Pesi?., 180,000; according to Pir?e R. El., 200,000). Their bones were strewn in heaps along the roads. According to the "Sefer ha-Yashar" (see Shemot), this event took place in the 180th year after the Israelites went to Egypt, when 30,000 infantry from the tribe of Ephraim left Egypt. The battle was waged near Gath. Because they rebelled against the word of God in leaving Egypt before the end of the captivity destined by God had arrived, all except ten were slain. The Philistines lost in the battle 20,000 men. The ten men who escaped from the battle returned to Egypt and related to their brethren what had happened to them. Ephraim, who was still alive, mourned over them many days. That the children of Israel might not see the bleached bones of the slain of Ephraim and return to Egypt, God led them to Canaan by circuitous ways (Ex. R. xx.). The slain Ephraimites were subsequently resuscitated by Ezekiel (Sanh. 92b). "