Our universe could end in ice but fire is a possibility.
The big crunch or phase shifts.
High energy deaths are also a possibility and from what we know, high energies could come again one day.
The big crunch.
The universe started expanding long ago. First The inflationary epoch just after the big bang. That slowed down when the "inflation force" degraded into the dark energy we have today. Once again it is accelerating but one day in the future we may see it slow down, stop and turn around. The big bang would then happen again and again crunching every time. We however see no signs of the expansion slowing down, or even accelerating slower.
Phase shift.
There might be different phases of empty space just like different phases of matter. When the average energy of the universe approaches 0 quantum tunneling may bring it out of a false bottom and into an even lower state. This could release huge amounts of energy throughout the entire universe. This could easily be enough energy to destroy all structures we observe today.
This could also happen in the field force of Dark energy or the Higgs field. They exist throughout the entire universe and only large amounts of energy can shift them.
The universe could end in fire but only a few conditions could let that happen.
https://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe
image source:www.nasa.gov/sites/default/files/images/635059main_hubble033012_full_full.jpg