Albeit that's always the possibility, I don't think that something similar will happen to Nets. Iirc Lakers had many issues that season with injuries and that's something you can't really control, then they changed the coach etc, it was a mess overall. So in case Durant/Harden/Kyrie gets injured, then I could see Nets struggling to reach playoffs but otherwise, I would really be surprised not to see them at least in the Conference final.
I also agree that the Nets have a great chance of reaching the final of the conference too, if any of the players (Durant, Harden and Irving) suffer an injury during the season, I think the chances would decrease considerably.
We also have to consider that if that happens,
reserve players will have to do their part to try to make up for this possible loss.
Bolded part could be a big issue for Nets. In order to get Harden they got rid of three players that had decent minutes up to that point: Allen, LaVert and Prince (no point counting Rodions Kurucs as he barely played). LaVert was their best player coming from the bench, scoring 18.5 ppg on less than 28 minutes per game. Check thier last two games since the trade and how bench performed; last night vs Bucks bench scored 15, and two night ago they scored 19 vs Magic.
All is good as long as those big 3 stay healthy, but if one of them gets injured, then its gg for Nets. But they knew the risks when they went into that trade.
I think he plays defense, but mainly he is more focused on scoring, instead of defense, you can see that in lots of hardens play, yes he got a block and got still but that's just in some plays if you see other star players they do all around, LeBron, KD, the Klaw, they do balance playing, that is why they easily saw hardens playing less defense, I think that's what hardens need to be better than before, he is already great but if he can play like them he will be more unstoppable.
He improved in that regard in the last few years, and he will probably focus even more on that aspect now in Nets because both Irving and Durant are very good offensively so it won't be just up to him to score.