No mythic reward

Hey OnrehabZ​,

To clarify, this would be a guaranteed set of Heirloom Shards if you reach 500 regular packs opened without getting one in packs prior to that point. Event packs do not count towards this limit.

Additionally, the free packs earned purely from leveling (not counting those from seasonal battle passes) comes out to 544 - this would be the total from account level 1 to account level 2000, the current cap. 

This would mean that while level ~650 is definitely a substantial amount of packs, it's nowhere near enough to hit that guaranteed heirloom purely from leveling. What will bump that up further for you would be any of the packs you've received in battle passes along the way or as event rewards (though not event packs), or any non-event packs you've purchased directly.

There's not an official tracker for this unfortunately, but the team does perform checks to make sure the system itself is still working properly - most recently here. There are some fansites that can help with tracking as well, but these may not be entirely accurate. 

If you've been playing pretty regularly since Season 1 and are level 650+ you're likely getting close to that point, though without knowing specific numbers of packs opened for each season I wouldn't be able to be more precise, sorry. Best of luck!