What's your opinion on a Christian staying behind to assist the tribulation saints?
I think it is bad idea, and I doubt it is an option for any believer to choose. The tribulation is not going to be a time for which any Christian would want to remain behind. The vast majority of believers will die during the seven-year tribulation.
The last person who spoke boldly of dying for his faith ended up denying his master three times before the night was out.
Now is the time to be a witness to the world. The seeds that are planted now in the hearts of the unsaved will quickly germinate on the other side of the rapture.
For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever"(1 Thessalonians 4:16-17).