We shall only know for sure when your putative 144,000 people finally show up, but I find it strange that Ephraim and Dan are missing, yet there are still twelve tribes. Ephraim and Dan, of course, are those tribes that were the centres for idolatry (1 Kings 12:27-29).I find no reason in Scripture to believe that the 144.000 in Revelation is a symbolic number. If you have some compelling biblical evidence to show why it is and must be symbolic . . .
But consider this: John 'hears' the number of those who are sealed (Revelation 7:4), but when he 'looks,' he sees 'a great multitude which no one could number' (Revelation 7:9). It is my contention that these are the same people. They are a covenant number that is known to God (the 12 tribes of Israel times the 12 apostles times as many as there are), but unknown to man.