That is a bad idea, especially since the device can be traced once it's used. Just checking quickly to see if data can be recovered should be fine, but the obligation is almost always to return a device that's been replaced once it's found.. Not returning it can be grounds for civil or criminal liability. For example, here are the US terms for Apple's Theft and Loss coverage through AIG:
https://www.aigtheftandloss.com/static/media/ExNY.72830d3f.pdf
AppleCare+ with Theft and Loss Program Summary and Disclosure
.......
Any recovery or salvage on a Loss will accrue entirely to Our benefit. Upon Our request, You will return to Us any damaged equipment. All Equipment which We replace is the property of Us and may be disabled, destroyed, or reused. We will not provide replacement equipment if You are in breach of the terms of this Certificate due to: failure to return damaged Equipment when requested in conjunction with a prior Loss; or, due to Your failure to satisfy the non-returned equipment charge or deductible on a prior Loss.