Hi @WendyThrive,
Thank you for your feedback, we've edited the original post for accuracy. Your client, the lessee, can claim depreciation for the term of their lease based on the effective life of the assets. Capital works can be depreciated at a rate of 2.5% - https://www.ato.gov.au/individuals-and-families/investments-and-assets/property-and-land/residential-rental-properties/rental-expenses/capital-expenses/work-out-your-capital-works-deductions
However, once the lease ceases, you're correct they're not entitled to this deduction upon disposal of (walking away from) these improvements, but the entitlement to the deduction reverts to the building owner. I have seen an alternative view that a CGT event (A1 or C2, depending on whether the lessor or lessee were deemed to be the owner) arises with an associated capital loss being the remaining un-deducted cost base of the improvements'.
If your client at the end of their lease removes items and remains the owner of these assets, they may need to complete a balancing adjustment based on the termination value of the capital asset. You can also refer to the link from RichATO's response.