Is the ending of Mark really scripture?

Is the ending of Mark really scripture?
Mark 16:9-20

      There is dispute over Mark 16:9-20 and whether or not it should be included in the New Testament.  It is found in many old manuscripts but is omitted in two of the earliest complete copies of the Bible known as the Vaticanus (350 AD) and Sinaiticus (375 AD).  Additionally, there is another ending to Mark in some old manuscripts that is substituted for 9-20.  The alternate ending reads as follows:

"And they promptly reported all these instructions to Peter and his companions. And after that, Jesus Himself sent out through them from east to west the sacred and imperishable proclamation of eternal salvation."

     Some scholars have asserted that the ending is in a different style than the rest of the gospel and that it contains 16-22 "non-marcan" words used in a "non-marcan" sense.  It seems to suggest that Jesus appeared in a different form (v. 12) which could be problematic since Jesus rose in the same body He died in (John 2:19-21).  Also, Mark 16:16 can be interpreted to mean that baptism is part of salvation.  It isn't as is testified by verses that teach justification by faith Rom. 5:1; 6:23; Eph. 2:8-9, etc.).  Whichever the case, the dispute is not settled and may never be.
     I am not here trying to undermine the authority of God's word nor state that Mark 16:9-20 is not authentic.  But, the fact remains that these 12 verses are under dispute and it is necessary to spotlight this issue when dealing with the historic reliability and inspiration of the New Testament manuscripts.  

The text of Mark 16:9-20

      "Now after He had risen early on the first day of the week, He first appeared to Mary Magdalene, from whom He had cast out seven demons. ¹⁰She went and reported to those who had been with Him, while they were mourning and weeping. ¹¹And when they heard that He was alive, and had been seen by her, they refused to believe it. 
     ¹²And after that, He appeared in a different form to two of them, while they were walking along on their way to the country. ¹³And they went away and reported it to the others, but they did not believe them either.
     ¹⁴And afterward He appeared to the eleven themselves as they were reclining at the table; and He reproached them for their unbelief and hardness of heart, because they had not believed those who had seen Him after He had risen. ¹⁵And He said to them, "Go into all the world and preach the gospel to all creation. ¹⁶"He who has believed and has been baptized shall be saved; but he who has disbelieved shall be condemned. ¹⁷"And these signs will accompany those who have believed: in My name they will cast out demons, they will speak with new tongues; ¹⁸they will pick up serpents, and if they drink any deadly poison, it shall not hurt them; they will lay hands on the sick, and they will recover."
     ¹⁹So then, when the Lord Jesus had spoken to them, He was received up into heaven, and sat down at the right hand of God. ²⁰And they went out and preached everywhere, while the Lord worked with them, and confirmed the word by the signs that followed," (NASB).