No. There is no sales number that really guarantees a sequel. It's really more of a corporate decision. Whether you think that a sequel would help the brandname or sustain it.

Remember more than half the time a sequel doesn't sell as well as an original, as normally the original is better and still sells over long periods of time.

 This.  It all comes down to whether or not the developers think they can profit on a sequel.  The original doesn't even necessarily need to have sold well.  Killzone is getting a sequel despite the first one's sales because Guerilla believes they will be able to sell a lot.

Brawl passed 1.3 mil 1st day right? Why does Kojima think MGS4 will break 1 mil first day? It seems highly unlikely. It's hyped. But not HALO hyped.

It will however break 1 mil first week.
Gta4 will break 1 mil the 1st hour!!! (i will make a bet on that!)

 No way to track that.

 The first Killzone sold well, it sold atleast 2.4mil copies.

@ De85 )

uhm.. Killzone sold over 2 million (it sold better in europe than in US) afaik, so I would be surprised, if it wasn't a financial success

 Metal Gear has a decent shot at going platinum on day one, especially since its arguably being hyped more than any other game in the series, with the possible exception of the first Metal Gear Solid game. I wouldn't necessarily bet on it, but I wouldn't discount it either. As to Kojima, I think a large part of it is sheer hope, since from everything I've heard, it's a damned expensive game to make. Didn't a Konami executive publicly say that it has to sell a million copies day one to ultimately make a profit?

As to Grand Theft Auto four...no takers.

 And on topic: some developers prefer not to make sequels to their games, no matter how much they sold, just because they value the game's artistic integrity over its profitability, and don't wish to cheapen it with an inferior sequel. And at the end of some rainbows, there's a little green man with a pot of gold just waiting for you.

 My bad, the database has it listed at 750k.  On closer inspection it doesn't have any data for Europe so that's probably what threw me off.

not always
depends

If Gears 2 would sell 1 million even in its first month it would probably be considered that the game bombed . Now looking at Carnival Games ... that game will probably be around even when FF20 will bomb :P