new Float:PosX[MAX_PLAYERS], Float:PosY[MAX_PLAYERS], Float:PosZ[MAX_PLAYERS], Spectating[MAX_PLAYERS];

//---Your command/script.
GetPlayerPos(playerid, PosX[playerid], PosY[playerid], PosZ[playerid]);
TogglePlayerSpectating(playerid, 1);
Spectating[playerid] = 1;
//SetPlayerCameraPos
//SetPlayerCameraLookAt
//etc., etc.

//---Your command to stop spectating.
TogglePlayerSpectating(playerid, 0);

//---OnPlayerSpawn
if(Spectating[playerid] >= 1)
{
    Spectating[playerid] = 0;
    SetPlayerPos(playerid,PosX[playerid],PosY[playerid],PosZ[playerid]);
}