There are different rules for a plan you're in currently, than one after you leave a company. Trying to roll over your current 401(k) to an IRA may not be allowed, or may at least be very tricky to accomplish.
Some employers offer a brokerage option where you can buy stocks or ETFs in your 401(k). In general target retirement funds do not offer ETF options, so if you want a one fund portfolio this won't work. But if you're looking to have a 3-fund portfolio (VTI, VXUS, BND) using Vanguard ETFs, it can work. This generally costs you an annual amount ($100 a year? it varies), and only for plans that offer a brokerage option.