Is it still possible for them to not give me the job at this stage? If
yes, what could be justifiable reasons for doing so ?
I'll assume you are in the US, and don't have any sort of signed contract or live in a jurisdiction having specific laws about this, and aren't in a union with specific rules about this.
In general, the company can back out at any point, and so can you.
You could even arrive the first day, and they could say "Sorry, this job is no longer available." They won't need to give you any further reason.
I could imagine that company conditions change and they no longer need your services. I could imagine that new data about you comes to light, and they decide they no longer want you.
That said, for all intents and purposes, this pretty much never happens. Once you reach that stage - unless the offer is contingent on some other action (like a successful background check that hasn't yet been completed, for example), or unless something far out of the ordinary happens - you should be good to go.
The closest I have seen is what happened at a former company. An individual was hired right out of college, with a starting date 2 months out. In the interim 2 months, layoffs occurred and all unfilled positions were closed, but the individual was never notified. He showed up for work as planned on the first day and only then learned what had happened. In this case, the company did the right thing by bringing him aboard anyway. They made a position for him in a different group. Eventually, he made it into the position he had originally hoped for.
Anything can happen - even after an offer is accepted. But usually there's nothing to worry about at that stage.