[[Appendix:Unicode]] subpage links are gone/broken

Yes, it was indeed intentional. I have done it, in fact, after I noticed you creating entries for Unicode code points, giving the Unicode character name as the definition. I think such entries should not be created, and other editors have agreed with me in a few discussions about the topic: Talk:⦰ and Wiktionary:Beer parlour/2015/January#Is documenting all Unicode characters within the scope of Wiktionary?; although there was some disagreement about what should be put in their stead.

I am of the opinion that:

• Wiktionary is a project that documents natural languages, not any particular computer encoding of them. There are already many websites presenting the Unicode character database in human-readable form, and there no real benefit to creating poor competition to them.
• Unicode code point names do poorly as definitions of glyphs they represent, and should not be remotely treated as such. They are as just as much of technical artefacts as the code point numbers, combining classes, bidirectional classes, etc.
• Emoji, dingbats and other symbols should be subject to the same attestation criteria as any other lexical item. It is better to be incomplete than unreliable.

So you also think it's reasonable to simply break linking with *everything* in Appendix:Unicode, even though it also contains single-character words such as in the CJK Unified Ideographs range? Then really, why have such an appendix at all if there is no individual character linking? I'm not really following your line of reasoning entirely.

If I tried the equivalent of {{#ifexist:X|[[X]]|X}}, it would run into expensive function limits quite quickly and fail to render. So it really is either all or nothing.

I have no idea why you would like to browse CJK characters through the Unicode appendix anyway; it is not like it is the most convenient way to do it, given their pretty much random placement.

Just because one person finds a method inconvenient doesn't mean everyone does. Unicode is a standard, and its ordering matters to things like CJKV characters; also, the placement is in radical-stroke order, not "pretty much random" as you attest. Perhaps you don't know as much about these things as you think you do?

Okay, I admit that I made that statement based on an extrapolation from my observations about placement of letters in Latin and Cyrillic scripts, which at this point are decided on a "wherever it fits" basis. I realise the analogy may not carry through completely, and Unicode Inc. may even attempt to maintain some sane ordering within individual allocation ranges. I can grant you that. (Even though you cannot rely on this property on a large scale: U+20000 has fewer strokes than U+4684. From that perspective, the placement really is random.)

On the other hand, this is still not the most convenient way to browse CJK characters, given that you only have a meaningless number next to the character itself in a smallish font, and a completely nondescriptive character name of the "CJK UNIFIED IDEOGRAPH-XXXXX"…

Anyway, there are some other reasons why I decided removing all links from that appendix was an overkill after all. I restored the links in Appendix:Unicode. Still, in the future please do not create entries of the kind that I mentioned.