Lost radio communication after take-off in IMC - what are my options?
The answers to these questions can be found in the AIM in section 6-4-1. All quotes are from that page.
To the first question, you should expect to receive a clearance to 8,000 feet twenty minutes after departure; therefore, don't climb above 4,000 until that time. If you are still in radio contact after 20:55, the &quot;expect&quot; portion of the clearance expires:

If the pilot received an “expect further clearance” containing a higher altitude to expect at a specified time or fix, maintain the highest of the following altitudes until that time/fix:
(1)   the last assigned altitude; or
(2)  the minimum altitude/flight level for IFR operations.
Upon reaching the time/fix specified, the pilot should commence climbing to the altitude advised to expect. If the radio failure occurs after the time/fix specified, the altitude to be expected is not applicable and the pilot should maintain an altitude consistent with 1 or 2 above.

For the second question, the answer comes down to the definition of &quot;briefly&quot;. Is your hole big enough for you to get under the clouds, and is the ceiling high enough that you can remain VMC to land? If so, you should do so. But if you just briefly see the ground, or aren't confident that you could safely fly VFR to a suitable airport, then you should maintain IFR and continue flying your clearance. You may inconvenience a few controllers, but if you leave your cleared route only to discover that your intended airport is socked in, getting back to your route to resume your original destination puts you potentially low to the ground, and not along the route that ATC is expecting you:

Pilots should recognize that operation under these conditions may unnecessarily as well as adversely affect other users of the airspace,
since ATC may be required to reroute or delay other users in order to
protect the failure aircraft. However, it is not intended that the requirement to “land as soon as practicable” be construed to mean “as soon as possible.” Pilots retain the prerogative of exercising their best judgment and are not required to land at an unauthorized airport, at an airport unsuitable for the type of aircraft flown, or to land only minutes short of their intended destination.

That said, VFR traffic should always be looking for other aircraft - with and without radio contact. Radios are not required equipment, at least at non-towered airports, so landing among VFR traffic without a radio should not be a big deal.