No, they can't. The likes of Palau are (barely) viable as sovereign countries, because at least the geographic size is as small as their populations.
It is absolutely, positively, completely impossible for 50K Greenlanders to by themselves maintain a the world's largest island, even aside from the completely frozen-over aspect. The $600M annual subsidy by Denmark does not include the funds Copenhagen spends on also running Greenland's foreign relations and defense. But in reality, Denmark spends a relative pittance on those things (like "six dog sleds" pittance); the vast majority of the cost of defending Greenland is borne by the US, as has been the case since 1940. Why should the US shoulder the burden without commensurate political power?