Other than Jim83.

In Japanese, if you don't know a particular Kanji, you can fake your way by writing out the word with hira/katakana. I do this all the time.

What could Chinese people do if they don't know a Kanji?

They don't have anything other than Kanji.

If you substitute another Kanji that sounds alike for the one you don't know, the other Kanji might have the same sound but a completely different meaning.

I guess there's more pressure to learn all the Kanjis.