public OnPlayerDisconnect(playerid,reason) 
{
    if(//check if the player id logged in here)
    {
        new Float:x, Float:y, Float:z;
        GetPlayerPos(playerid,x,y,z);
        //save your floats using whatever method you're using now
    }
    return 1;
}
public OnPlayerSpawn(playerid)
{
    if(//check if the player has logged in and this is their first time spawning)
    {
        new Float:x, Float:y, Float:z;
        //load the data here
        SetPlayerPos(playerid,x,y,z);
    }
    return 1;
}