Answer
If you downloaded any games with your Steam account, Steam will not delete your account. On the other hand, Steam does not charge account users for inactive use, so you can basically just let your account remain dormant.
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Does steam delete inactive accounts?
If you downloaded any games with your Steam account, Steam will not delete your account. On the other hand, Steam does not charge account users for inactive use, so you can basically just let your account remain dormant.