Help! I need dental advice regarding my current molar situation

[gsp111]

Hi,

A month ago the crown of my upper left 2nd molar cracked in half to the gum line due to it being severely decayed.

I booked an appointment to see a dentist and within the first 5 minutes of completing the x-ray she said I need root canal or extraction. Immediately, I went back home and booked to see a different dentist at a different dental clinic. The second dentist took an x-ray and told me to come back a week later. When I returned, she said that it's "a big question mark" and that she can attempt to save it by filling it.

What she did was:
- Remove the remaining amalgam from the split tooth
- Remove the decay
- Put calcium hydroxide (I think) on the base of the filling and did a pulp cap
- She then used an amalgam pin (or dental pin) and proceeded to restore the tooth with amalgam

It's been a month now, and the only problem with this filling is that I have sensitivity to cold consumables. Hot consumables such as tea are not an issue at all. The sensitivity I experience lasts for literally less than 2 seconds and only occurs when I haven't consumed anything cold for a while. Other than this, everything seems to be okay.

Now, what I am worried about is the life of this tooth, the impact it may have on the rest of my teeth if one day I have to have it removed and if orthodontic treatment is not worth getting with what may be a short living tooth.

The questions I have in specific (there are quite a few of them!) are:

Is it certain that I will eventually need root canal or extraction in the future? Or can a filling such as this last if I look after my teeth well?

If for whatever reason I have the tooth extracted, what impact will it have on my surrounding teeth (and facial structure)? Will "super-eruption" occur with this particular tooth extracted? And will I need dental implants?

Would orthodontic treatment (braces) be a waste of money at this stage since it's possible that I will lose a molar? I want to get braces but I'm scared that if I ever have the tooth extracted(*) all of my teeth will start to shift and my money will be thrown down the drain.

* The reason why I do not wish to have root canal with a crown is because of the toxicity of it. I am aware amalgam is no better, but I chose it in this situation because of its durability.

Thank you so much for reading, and many thanks in advance to anyone who answers my questions. I apologize for the relatively long post!