I once heard that if I get enlightened everybody gets enlightened. Is this something you consider to be true?
Also, if anybody else gets enlightened, I would not get enlightened, so I cant just wait for someone else to enlighten me, I have to do it myself. Is this correct?
There are statements like this, particularly in Western expressions of Zen, and some other Mahayana traditions, but it is certainly not a position that all Mahayana, or even most Mahayana, would assert.
Personally, I think it is a development, and a rather dubious one of that, of another idea, which is more fundamental to most of the Mahayana, and some non-Mahayana schools too. That idea is that at the bottom line, the essential nature of all phenomena is the same. This is related to dependent origination.
eg. the nature of a buddha is that of dependent origination, one becomes a buddha due to conditions; likewise, even unenlightened beings are also in the same category of being subject to dependent origination. This is their "suchness", which is "profound".
However, unenlightened beings do not know this, but once one knows it, one becomes a Buddha. ie. knowings "suchness" (tathata), one becomes a "thus come one" (tathagata).
Therefore, rather than "When one becomes a Buddha, everyone becomes a Buddha", it is more the case of "When one becomes a Buddha, one knows that the nature of a Buddha is the same as the nature of an unenlightened being." And knowing that all beings are dependently originated, they also know that there is the possibility for them to become enlightened, too.
The mistake is to say: "Because the nature of a Buddha is suchness, and because the nature of an unenlightened being is also suchness, therefore an unenlightened being is also a Buddha." Logical fallacy. eg. try "Because the color of a sheet of paper is white, and because the color of a polar bear is white, therefore a polar bear is a sheet of paper." oops.
Another problem is one (but not all) later East Asian interpretation of "Mind Only", which is also common in the West (due to Jungian notions of a the sub-conscious, and other western views). It suggests that when one's mind is purified, then all minds are purified, because all living beings have the same "One Mind". This idea of "One Mind" as something shared by all beings, a cosmic Mind accessible by all, is not the original meaning in the Yogacara school. There are certain Brahmanic influences, particularly in the later period.
Obviously, the problem with this idea, is that then when the first Buddha was enlightened, we would all be enlightened already! No need to practice, no need to teach Dharma, etc. This is extremely problematic, and similar parallels in Brahmanic and Sramanic atman systems have the same problem. It leads to inactivity in the bad sense. Do what you want!
The "originally enlightened but don't know it" issue is an attempt to answer this problem. But to me, it has so many problems that it is barely worth considering. They should take a few steps back and work it out, rather than proceeding with an error, and trying to fix it.