[BigGroter]

Yup, you have to use GetPlayerPos().
You can try defining the old positions as a global variable.

Code:

new Float:OldPos[3]; //under defines


CMD:fix(playerid,params[])
{
    new Float:health;
    new veh;
    GetPlayerPos(playerid, OldPos[0], OldPos[1], OldPos[2]);
    veh = GetPlayerVehicleID(playerid);
    GetVehicleHealth(veh, health);
    if(!IsPlayerInAnyVehicle(playerid)) return SendClientMessage(playerid, red, "You need to be in a vehicle to use this");
    else if(health > 999) return SendClientMessage(playerid,red,"Your vehicles at 100%");
    SetTimer("repairtime",10000,false);
    SendClientMessage(playerid,green,"Help will arrive in 10 seconds. Please wait.");
    return 1;
}

Then create a timer that checks if OldPos[0], OldPos[1] and OldPos[2] are equal to the players current positon. (Which you get with GetPlayerPos()