Does Reformed Baptist Protestantism reject Annihilationism? John Stott argued against the eternal punishment of unbelievers whereas J I Packer argued for the view that Jesus Christ warned of the eternal punishment of those who reject himself and his gospel.
What is the current view of Reformed Baptist Protestantism on this matter ?
The traditional view of Reformed Baptists (and the Reformed view more generally, including of Anglicans) is that of eternal punishment.
Take, for example, the Westminster Confession of Faith. This taken from Chapter VI:

Chapter VI.
Of the Fall of Man, of Sin, and of the Punishment thereof.
... VI. Every sin, both original and actual, being a transgression of the righteous law of God, and contrary thereunto,(n) doth, in its own nature, bring guilt upon the sinner;(o) whereby he is bound over to the wrath of God,(p) and curse of the law,(q) and so made subject to death,(r) with all miseries spiritual,(s) temporal,(t) and eternal.(u)

This is consonant with other statements of faith, for example the Anglican Book of Homilies, book 1, homily II &quot;On the Misery of Mankind&quot;:

Thus we haue heard how euill we be of our selues, how of our selues, and by our selues, we haue no goodnes, helpe nor saluation, but contrariwise, sinne, damnation, and death euerlasting

This has been challenged on a number of occasions, such as Anglican Ian Paul. Various books and articles have also been written defending the traditional view, such as Hell Under Fire, written from within a Reformed tradition.
So I would say there are those within Reformed circles who question eternal punishment and hold to something more like annihilationism. But this is not the traditional, confessional view, and there are many in the tradition who defend the traditional view.