First, Sandbox solutions that contain code have already been deactivated in SharePoint Online. They aren't just deprecated, they are already disabled. You can still use Sandbox solutions for declarative XML content, but not for DLLs.
There are no published plans to deprecate the use of WSP (Farm Solutions) in on-premises environments, but they are not and never will be available in Office 365. So although you can continue to use them in your On-premises environment, if your eventual
goal is to move to Online then you should start planning to rewrite all your WSPs to use some form of Client Side code, either Add-ins or SharePoint Framework.
Paul Stork SharePoint Server MVP
Owner/Principal Architect: Don't Pa..Panic Consulting
Blog: http://dontpapanic.com/blog
Twitter: Follow @pstork
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