Blind PassengerWell that an...interesting background story. Though that reveals a fact that seems a bit confusing. since, if Streaky left Krypton before the "big Boom", and Krypto knew her from there, that means both pets are at least Clark's age which...I guess is theoretically possible given we talk alien animals here, but still a bit mind-blowing.
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Streaky was indeed fortunate enough to leave before the Big Boom! But he was definitely young and as a kitten he is prone to explore and look for squeaky snacks in all manner of places. Let's face it, that's what furballs do!

As a Kryptonian with a different DNA structure, it is possible he would live much longer than a Earth kitty.
Did Streaky take someone's place on the ship? No. It was tiny, only big enough to carry a cat. Since Kara was older than her cousin, it is doubtful Zor-El built it for her escape. It was simply a very sophisticated prototype.