They shouldn't (and probabaly wont) die due to the higher temperature no. But it will speed up their life cycle leading to an earlier death (though still very much in the distant future). And as said, it's not really recommended.
And if I had to keep guppies and goldies together I would rather heat the water for the guppies knowing the goldfish will be ok if it's a bit warmer rather than have the guppies being too cold.
Having said that, you probably don't need to heat to 25C, the guppies should be fine at 22/23C