Would it be possible to convert this adventure to the 5th edition rule set?
“Fantasy is escapist, and that is its glory. If a soldier is imprisioned by the enemy, don't we consider it his duty to escape?. . .If we value the freedom of mind and soul, if we're partisans of liberty, then it's our plain duty to escape, and to take as many people with us as we can!” #8213; J.R.R. Tolkien
Would it be possible to convert this adventure to the 5th edition rule set?
You can convert any adventure from any ruleset to any other... The question is how difficult it will be and how much work are you willing to put into it. Some are obviously easier to convert than others.
It's probably more in need of a rewrite than a conversion. I redid the night below for FR, it's a lot of fun trying to think up motivation for events from the evil persons point of view
one big thing in these types of conversions is the types of monsters used in one edition have noticeable power differences between editions. For instance, 3e giants are noticeably more powerful than their 1e and 2e versions.
The real problem with throne of bloodstone will come at the end - you battle your way through powerful demon lords. I recommend leaving it in the past - instead build off of it. What if I told you there were rumors that Zhengi, while defeated, was not actually destroyed and he had set his sights once again on conquest?