What do Chinese people do if they forget how to write a character?
As a native Chinese speaker, I sometimes replace the forgotten phrase with another one which has same meaning. Sometimes I even rewrite the whole sentence to avoid writing some hard characters.

By the way, since there are a lot of Chinese characters has the same pronunciation (ex: 意義/異議). The input programs are also very error-prone to select correct characters. Some people will just use wrong characters with the similar pronunciation because they are too lazy to correct them. This is why you can see some common mistakes like 因該 instead of 應該.