Okay so I forgot to take this tree in when the temperature dropped, and now it is not very happy

Do you think there's still time to save it or is it time to let go?

Hard to say. Freeze damage to foliage is an entirely different matter compared to root temperatures below killing lows. There's only 1 degree of dead,

For now, it's best to take up a wait-and-see position. After a week or so, there is no reason not to remove the entirely dead leaves. Allow any leaves showing green after that time to remain on the plant - they will serve as a source of photosynthate (food/ glucose) and the plant might be able to reclaim mobile nutrients and other biocompounds during the process of resorption. If, after a month you see no indication of new growth, it's probably lost all viability. Be aware that the loss of all or nearly all foliage will severely limit how much water the plant needs, so be very careful to avoid over-watering. No fertilizer during the initial stage of recovery; after that, how you fertilize depends on your watering habits and what the current soil nutrient level might be.

If we knew how long and to what temperature it was exposed, an educated guess might be made about its chance of rebounding.

Al

Yes, 'what he said'
so if you are OK watching and waiting for many months for it to get back as it was, you may. If you'll be excited with any new growth and seeing it rebound, keep it. If it will depress you looking at a struggling plant for months, let it go.

I just feel bad for people who feel so bad about sick plants, and look at them every day feeling like bad plant parents.

Still time to save it is a mute point. It's either dead or not dead. How long was it in the cold? As long as the soil in the pot didn't freeze solid it should if nothing else come back from the roots. There are different degrees of "freezing". If it was only in the cold a short while and just the foliage got froze then it will put out new foliage. If the foliage and upper part of trunks got froze they will turn black and fall off but the lower part of the trunks will put out new foliage. If everything above the soil got froze but the roots didn't then it will regrow from the roots. If everything got froze including the roots pitch it in the compost pile it's toast.