Hydrazones are usually very stable towards solvolysis, and conversion to the ketone can require vigorous conditions. Also, aldehydic hydrazones often instead disproportionate to a nitrile and amine.  
Two principal workup environments are common: oxidation and solvolysis.  Reductive conversions are possible with low-valent transition metals, but remained relatively unstudied .
Oxidative cleavage has high yields and is most frequently used.  Ozone or singlet oxygen can ozonolyze the diazene bond (and any olefinic moieties present), leaving a carbonyl, a nitrosamine, and dioxygen.   Lemieuxs gentler oxidation tolerates acetals and benzyl ethers.  Peroxide reagents (e.g. NaBO, (tBuNSO), or m'-ClBzOH) cleave the hydrazone with varying speeds, selectivities, and mechanisms, but the Baeyer-Villiger oxidation is a common side-reaction.  High-valent transition metal oxyhalides (e.g. WF, CoF, MoOCl) appear to primarily cleave via radicals.  All except ozone and singlet oxygen generate nitriles from aldehydic hydrazones, either as the major or a substantial minor product.  
Certain electrophiles also elicit nitriles: chloroformates, strongly-activated alkynes, or methyl iodide and a hindered base.  Methyl iodide is also useful for hydrolysis: the alkylated hydrazonium iodide easily hydrolyzes to a carbonyl and hydrazoform, and air cleaves the hydrazoform to the hydrazine and carbon dioxide.  
Indeed, a wide variety of acids promote hydrolysis.  Bismuth trichloride cleaves arbitrary hydrazones in a microwave.  Oxalic acid abstracts hydrazine from ketonic hydrazones; the oxalate adduct then decomposes to the original auxiliary in aqueous base.  Silica gel hydrolyzes exquisitely acid-sensitive substrates, but is too weak to affect ketonic hydrazones adjacent to a primary carbon.  Ketonic hydrazones adjacent to a secondary or tertiary carbon hydrolyze in the presence of catalytic cupric salts; that procedure also preserves substrates disturbed by oxidants or strong acids.  
Boron trifluoride etherate catalyzes thioketalization, and Baker's yeast will hydrolyze non-bioactive substrates.  
Hydrazone carbamates are cleaved much more readily than their parent hydrazones: para-toluenesulfonic acid affords the corresponding ketones in near-quantitative yields.