In the scenario that was mentioned, because one still catches the congregational prayer one should not leave the highly rewarded act of helping another brother also attend. Having said this, because there is also great reward in attending the first rakaah one should perhaps start one's journey earlier and if this is not possible then make the intention of making the first rakaah. Inshallah, Allah will not deprive you of its reward especially because, along with having a firm intention of catching the first rakaaah, you were busy in helping another Muslim brother.