Why do Completed topics lose status overnight? As is, I'll never obtain a 2nd tree.
No, but it's best to strengthen topics from time to time. You can complete the tree without all skills being gold, but when it reads 3/5 on the strength bar next to the circle, you know it's time for a light practice. If it reads 2/5 or 1/5, you may want to spend some time on the topic. It is a good idea to strengthen what you need, but as a general rule you should practice weak topics/skills. By the way, you may want to read the article on rate of decaying in the Unofficial Wikia. If you do not use the "hints" that you get when you hover (This action is known as Peeking) , the skill will not decay as quickly. Hope this helped.