our robot descendants won't care about the long timescales. There's plenty they could do, or they could even power down for a few million years.
Would it be OK if the robots brought a dog along?
The rest of our fellow animal companions on this earth are thousand times better than any robot. If I'm forced to choose one of them, I wouldn't choose a dog, I'd go for one of the apes, octopus, crow, or maybe even a dolphin. But I'm fairly sure if they're given the option they'll rather stay here.