Under certain circumstances a copy of a will rather than the original, may be admitted to probate as the last valid will of the deceased.
The competing claimants will typically argue that there is a presumption of revocation when the original will cannot be produced.
There is more information on this topic under my blog heading of lost wills.
In short reasons for judgement, Canada Trust v MacMillan 2016 BCSC 1909 sets out a situation where the court was satisfied by evidence that the will maker executed a last will that had become lost due to changes in the law firms that held the will. Evidence was also led that she was mentally capable at the time the will was signed, as it was argues she had suffered from mental illness for much of her life.