The Bible says it’s appointed unto man once to die. What about the people who were raised from the dead, like Lazarus?

Being raised from the dead is a miracle.  A miracle by definition is something that goes against the laws of nature established by God in the beginning.  The laws of nature established by God in the beginning appoint death to come to mankind once (Heb. 9:27).  Miraculous resurrection from the dead goes against that law, thus allowing people like Lazarus and Jairus’ daughter to be the exception to the rule.

After their miraculous resurrection was completed, they would again be subject to natural law and thus eventually die without resurrection until judgment comes as God also decreed (John 12:10-11; Heb. 9:27; cf. 1 Thess. 4:13-18).  Jesus is called “the firstfruits of those who have fallen asleep” (1 Cor. 15:20, 23; Rev. 1:5; Col. 1:18) because He is the first to die and be raised never to die again (Rev. 1:18).  At judgment the faithful will likewise be raised never to die again.