The will is still valid.
S20 Wills Act 1837 provides
No will or codicil, or any part thereof shall be revoked otherwise than as aforesaid, or by another will or codicil executed in manner herein-before required, or by some writing declaring an intention to revoke the same and executed in the matter in which a will is herein-before required to be executed, or by the burning, tearing, or otherwise destroying the same by the testator, or by some person in his presence and by his direction, with the intention of revoking the same.
The important bit is the "burning, tearing or otherwise destroying the same BY THE TESTATOR, OR BY SOME PERSON IN HIS PRESENCE". Neither happened in this case.
You need to act quickly.
First lodge a caveat with the Probate Registry immediately - this prevents them obtaining the Grant of Representation, it is a simple form that you fill in but you MUST get all the details absolutely correct. Secondly take legal advice (preferably from a member of ACTAPS or STEP) - you may need an injunction to prevent any further dissipation of the assets.
There are also issues here with professional negligence of the solicitor - so he should be joined in any action since I would expect his PI insurance to pay the costs.
s20 seems extremely clear on the point. However, I will check the relevant case law a bit later just to confirm the position.